IMT Institutional Repository: No conditions. Results ordered -Date Deposited. 2023-06-03T05:10:05ZEPrintshttp://eprints.imtlucca.it/images/logowhite.pnghttp://eprints.imtlucca.it/2016-03-23T12:27:26Z2016-09-13T10:13:21Zhttp://eprints.imtlucca.it/id/eprint/3314This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/33142016-03-23T12:27:26ZPharmacological Modulation of Prefrontal Cortical Activity During a Working Memory Task in Young and Older Humans: A PET Study With PhysostigmineOBJECTIVE: Age-associated cholinergic dysfunction may contribute to the cognitive decline observed during aging, including a decline in working memory. The current study was designed to determine how healthy aging influences the neural response to working memory before and during pharmacological potentiation of the cholinergic system. METHOD: In 13 young and 13 older healthy volunteers, regional cerebral blood flow (rCBF) was measured by using [15O]H2O and positron emission tomography across 10 scans that alternated between a working-memory-for-faces task and rest. In all subjects, the first two scans were obtained during intravenous saline infusion. Seven young and eight older subjects then received intravenous infusion of physostigmine, a cholinesterase inhibitor, and the remaining six young and five older subjects continued to receive saline. RESULTS: In the placebo condition, task-specific rCBF increases in prefrontal regions were observed in the right middle and inferior frontal cortices in young subjects and in more anterior and ventral prefrontal regions in older individuals. Physostigmine during the working memory task significantly improved performance in both age groups. The right prefrontal regions that were selectively recruited in each age group during the placebo condition showed significantly lower rCBF during physostigmine administration. CONCLUSIONS: Cholinergic enhancement does not affect structurally defined cortical regions but rather modulates neural activity in functionally defined regions, that is, in task-related prefrontal cortical areas that are selectively and distinctively recruited in young and older subjects.Ulderico FreoEmiliano Ricciardiemiliano.ricciardi@imtlucca.itPietro Pietrinipietro.pietrini@imtlucca.itMark B. SchapiroStanley I. RapoportMaura L. Furey2016-03-23T12:25:33Z2016-05-11T11:08:05Zhttp://eprints.imtlucca.it/id/eprint/3313This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/33132016-03-23T12:25:33ZSlow wave and rem sleep mechanisms are differently altered in hereditary pick disease associated with the TAU G389R mutationSleep disturbances are found in the course of most dementing syndromes. We report a longitudinal polysomnographic and 18FDG-PET study in a 38-year-old male with FTDP17 carrying the Tau gene mutation G389R. All-night sleep EEG and wake cerebral glucose metabolism at rest (eyes/ears covered) of the preceding day were studied twice, eight months (Night 1; PET 1) and sixteen months (Night 2; PET 2) after the initial neurological evaluation. The Night 1 study showed sleep fragmentation associated to a short REM latency and a severe reduction of slow wave sleep, with relatively preserved NREM-REM sleep cycles; daytime PET 1 revealed severe cerebral glucose metabolic reductions in frontal and temporal areas, with relative preservation of remaining cortical regions and subcortical structures. On Night 2, the total sleep time was less than 5 hours, delta sleep and REM latency remained shortened and only two sleep cycles could be identified; daytime PET 2 exam revealed a greater cortical metabolic impairment and an involvement of subcortical brain regions as compared to PET 1. Post-mortem neuropathological data showed severe neuronal loss, spongiosis and gliosis that were mostly marked in cortical layers I, II, V and VI. In vivo, neurometabolic and post-mortem neuropathological data are consistent with and indicative of a severe dysfunction of intra- and trans-hemispheric regional connectivity and of cortico-thalamic circuits. These findings suggest that the decreased cortical and subcortical connectivity may have been the main pathophysiological mechanism responsible for delta sleep reduction and the cognitive decline.Angelo GemignaniPietro Pietrinipietro.pietrini@imtlucca.itJill R. MurrellB.S. GlazierPaolo ZoloMario GuazzelliBernardino Ghetti2016-03-23T12:04:49Z2016-09-13T10:11:38Zhttp://eprints.imtlucca.it/id/eprint/3311This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/33112016-03-23T12:04:49ZStudy of Reading Processes with ERPs and ER-FMRISilvia CasarottoA.M. BianchiSergio CeruttiDaniela BoninoClaudio GentiliEmiliano Ricciardiemiliano.ricciardi@imtlucca.itLorenzo SaniNicola VanelloMario GuazzelliPietro Pietrinipietro.pietrini@imtlucca.itLuigi LandiniGiuseppe A. Chiarenza2016-03-23T11:57:59Z2016-09-13T10:14:13Zhttp://eprints.imtlucca.it/id/eprint/3310This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/33102016-03-23T11:57:59ZVisual and tactile spatial discrimination activates the dorsal cortical pathway: a fMRI study in sighted and congenitally blind humansEmiliano Ricciardiemiliano.ricciardi@imtlucca.itDaniela BoninoLorenzo SaniClaudio GentiliNicola VanelloLuigi LandiniMario GuazzelliTomaso VecchiPietro Pietrinipietro.pietrini@imtlucca.it2016-03-23T10:54:48Z2016-09-13T10:14:50Zhttp://eprints.imtlucca.it/id/eprint/3309This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/33092016-03-23T10:54:48ZSupramodal organization in the "visual" cortical pathways as assessed by functional magnetic resonance in humansEmiliano Ricciardiemiliano.ricciardi@imtlucca.itNicola VanelloDaniela BoninoClaudio GentiliLorenzo SaniSabrina DantiNicola SgambelluriJames V. HaxbyLuigi LandiniTomaso VecchiMario GuazzelliAntonio BicchiPietro Pietrinipietro.pietrini@imtlucca.it2016-03-23T10:46:51Z2016-09-13T10:13:48Zhttp://eprints.imtlucca.it/id/eprint/3308This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/33082016-03-23T10:46:51ZFacial expression representation in the superior temporal sulcus and in fusiform gyrus: an fMRI studyMaria Ida GobbiniClaudio GentiliPietro Pietrinipietro.pietrini@imtlucca.itEmiliano Ricciardiemiliano.ricciardi@imtlucca.itNicola VanelloMario GuazzelliJames V. Haxby2016-03-23T10:44:12Z2016-09-13T10:15:02Zhttp://eprints.imtlucca.it/id/eprint/3307This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/33072016-03-23T10:44:12ZOptic and tactile flow: does a supramodal response exist?It is widely accepted [Morrone et al. Nature Neuroscience, 2000] that particular cortical areas like MT/V5 respond to optic flow stimuli. In order to test the hypothesis that the MT+ complex might also share a supramodal organization, we measured the neural response evoked during visual and tactile perception of coherently moving dot patterns (optic and tactile flows) in sighted and blind subjects by using functional magnetic resonance imaging. In particular a group of volunteers were asked to see and touch, during distinct trials, random distribution of dot patterns while moving in circular and translational direction. An ad hoc designed device made of nonmagnetic material was used. Both tactile and visual motion perception consistently activated MT+. In order to exclude the hypothesis that activation in visual cortical areas during tactile discrimination tasks might be attributed merely to visual imagery, tactile stimuli were presented to blind adults, confirming the activation of MT+ complex as well. Moreover, in order to assess the conjecture of supramodality of flow a magneto-compatible haptic display based on the contact area spread rate paradigm (specific aspect of tactile flow) was realized and used in fMRI experiment for investigating the neural activity elicited by tactile flow, providing satisfactory results.Enzo Pasquale ScilingoEmiliano Ricciardiemiliano.ricciardi@imtlucca.itPietro Pietrinipietro.pietrini@imtlucca.itAntonio Bicchi2016-03-23T10:34:11Z2016-09-13T10:14:39Zhttp://eprints.imtlucca.it/id/eprint/3306This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/33062016-03-23T10:34:11ZSupramodal response of human MT+ complex to visual and tactile perception of flow as demonstrated by fMRI studies in sighted and congenitally blind individualsEmiliano Ricciardiemiliano.ricciardi@imtlucca.itLorenzo SaniClaudio GentiliNicola VanelloJames V. HaxbyLuigi LandiniAntonio BicchiPietro Pietrinipietro.pietrini@imtlucca.it2016-03-23T10:19:49Z2016-09-13T10:13:35Zhttp://eprints.imtlucca.it/id/eprint/3305This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/33052016-03-23T10:19:49ZNeural correlates of working memory during visual and tactile spatial discrimination in sighted and congenitally-blind subjectsClaudio GentiliDaniela BoninoEmiliano Ricciardiemiliano.ricciardi@imtlucca.itLorenzo SaniMario GuazzelliPietro Pietrinipietro.pietrini@imtlucca.itTomaso Vecchi2016-03-23T10:17:52Z2016-09-13T10:11:22Zhttp://eprints.imtlucca.it/id/eprint/3304This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/33042016-03-23T10:17:52ZSupramodal cortical organization of the dorsal stream during visual and tactile spatial discrimination in sighted and congenitally-blind subjectsDaniela BoninoEmiliano Ricciardiemiliano.ricciardi@imtlucca.itLorenzo SaniClaudio GentiliLuigi LandiniMario GuazzelliTomaso VecchiPietro Pietrinipietro.pietrini@imtlucca.it2016-03-23T10:11:37Z2016-09-13T10:14:28Zhttp://eprints.imtlucca.it/id/eprint/3303This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/33032016-03-23T10:11:37ZSupramodal organization in the visual cortical pathways in sighted and blind individualsEmiliano Ricciardiemiliano.ricciardi@imtlucca.itClaudio GentiliNicola VanelloLorenzo SaniMario GuazzelliLuigi LandiniPietro Pietrinipietro.pietrini@imtlucca.it2016-02-29T12:03:35Z2016-09-13T10:11:11Zhttp://eprints.imtlucca.it/id/eprint/3167This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/31672016-02-29T12:03:35ZEmpathy modulates mirror system recruitment in
sighted and congenitally blind individualsDaniela BoninoEmiliano Ricciardiemiliano.ricciardi@imtlucca.itMario GuazzelliPietro Pietrinipietro.pietrini@imtlucca.it2016-02-29T12:01:07Z2016-09-13T10:13:03Zhttp://eprints.imtlucca.it/id/eprint/3166This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/31662016-02-29T12:01:07ZBrain correlates of functional and dysfunctional
beliefs: an fmrI study of cognitive reappraisalIoana CristeaClaudio GentiliEmiliano Ricciardiemiliano.ricciardi@imtlucca.itGiuseppina RotaDaniela BoninoDaniel DavidPietro Pietrinipietro.pietrini@imtlucca.itMario Guazzelli2016-02-29T11:43:18Z2016-09-13T10:13:58Zhttp://eprints.imtlucca.it/id/eprint/3165This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/31652016-02-29T11:43:18ZWhat have we learned about seeing from the blind?A. Pascual-LeonePietro Pietrinipietro.pietrini@imtlucca.itEmiliano Ricciardiemiliano.ricciardi@imtlucca.itK. SathianB. RoederA. AmediM. LassondeL. Merabet2015-02-06T11:52:22Z2015-02-06T14:06:29Zhttp://eprints.imtlucca.it/id/eprint/2560This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/25602015-02-06T11:52:22ZA Markov model of a freerider in a BitTorrent P2P networkBitTorrent is today one of the largest P2P systems which allows file sharing for Internet users. Very little effort has been dedicated to this target up to now. The goal of this paper is to develop an analytical model of a free-rider in a BitTorrent network. Unlike previous analytical models which capture the behavior of the network as a whole, the proposed model is able to analyze the performance from the user perspective. The model is applied to a case study to evaluate performance in a real case, and to obtain some insights into the influence of BitTorrent parameters on system performance.Mario BarberaAlfio LombardoGiovanni SchembraMirco Tribastonemirco.tribastone@imtlucca.it2014-12-02T14:12:11Z2014-12-18T13:57:58Zhttp://eprints.imtlucca.it/id/eprint/2378This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/23782014-12-02T14:12:11ZUnderlying scale-free trees in complex networksWe investigate the properties of two relatively different spanning trees of complex networks, so-called “communication kernel" and “response network". First, for the communication kernel, we construct spanning trees carrying a maximum total weight of edges that is given by average traffic, which is defined as edge betweenness centrality. It is found that the resulting spanning tree plays an important role in communication between vertices. We also find that the degree distribution of spanning trees shows scale-free behavior for many model and real-world networks and the degree of the spanning trees has strong correlation with their original network topology. For the response network, we launch an attack on a single vertex which can drastically change the communication pattern between vertices of networks. By using minimum spanning tree technique, we construct the response network based on the measurement of the betweenness centrality changes due to a vertex removal. We find that the degree distribution of the response network indicates the scale-free behavior as well as that of the communication kernel. Interestingly, these two minimum spanning trees from different methods not only have same scale-free behavior but overlap each other in their structures. This fact indicates that the complex network has a concrete skeleton, scale-free tree, as a basic structure. Dong-Hee KimSeung-Woo SonYong-Yeol AhnP.-J. KimYoung-Ho Eomyoungho.eom@imtlucca.itHawoong Jeong2014-10-07T13:25:24Z2015-04-08T10:37:32Zhttp://eprints.imtlucca.it/id/eprint/2291This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/22912014-10-07T13:25:24ZThe spatial logic model checker user's manual: version 1.0Hugo Torres Vieirahugo.torresvieira@imtlucca.itLuis CairesRubens Viegas2014-07-08T13:48:09Z2014-07-08T13:48:09Zhttp://eprints.imtlucca.it/id/eprint/2252This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/22522014-07-08T13:48:09ZNon-smooth model predictive control: stability and applications to hybrid systems In this report we investigate the stability of hybrid systems in closed-loop with Model Predictive Controllers (MPC) and we derive a priori sufficient conditions for Lyapunov asymptotic stability and exponential stability. A general theory is presented which proves that Lyapunov stability is achieved for both terminal cost and constraint set and terminal equality constraint hybrid MPC, even though the considered Lyapunov function and the system dynamics may be discontinuous. For particular choices of MPC criteria and constrained Piecewise Affine (PWA) systems as the prediction models we develop novel algorithms for computing the terminal cost and the terminal constraint set. For a quadratic MPC cost, the stabilization conditions translate into a linear matrix inequality while, for an ∞-norm based MPC cost, they are obtained as ∞-norm inequalities. It is shown that by using ∞-norms, the terminal constraint set is automatically obtained as a polyhedron or a finite union of polyhedra by taking a sublevel set of the calculated terminal cost function. New algorithms are developed for calculating polyhedral or piecewise polyhedral positively invariant sets for PWA systems. In this manner, the on-line optimization problem leads to a mixed integer quadratic programming problem or to a mixed integer linear programming problem, which can be solved by standard optimization tools. Several examples illustrate the effectiveness of the developed methodology.Mircea LazarW.P.M.H. HeemelsSiep WeilandAlberto Bemporadalberto.bemporad@imtlucca.it2014-07-08T13:40:37Z2014-07-08T13:40:37Zhttp://eprints.imtlucca.it/id/eprint/2251This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/22512014-07-08T13:40:37ZAn algorithm for PWL approximations of nonlinear functionsIn this report we provide some technical details for some of the results appeared in [Alessio et al.(2005)]. In the first section we provide the proof of continuity of the PPWA function computed with the ”squaring the circle” algorithm stated in ACC 06. Then, we analyze the complexity of the previous algorithm, in terms of the desired level of accuracy in the approximation of the PPWA function.Alessandro AlessioAlberto Bemporadalberto.bemporad@imtlucca.itB. AddisAlessandro Pasini2013-11-25T10:19:29Z2014-10-09T09:20:26Zhttp://eprints.imtlucca.it/id/eprint/1939This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/19392013-11-25T10:19:29ZOn the asymptotic stress field in angularly nonhomogeneous materialsThe problem of multi-material junctions composed of angularly nonhomogeneous elastic wedges in plane elasticity is addressed. For this new type of grading the governing equation for the Airy stress function is derived and, by applying the eigenfunction expansion method, a fourth-order ODE with nonconstant coefficients for the eigenequation is obtained. The solution to this ODE permits the formulation of an eigenvalue problem similar to that valid for material junctions between homogenous different materials. It is mathematically demonstrated that the angular grading influences the order of the stress-singularity. The potentials of the use of this new class of materials in joining technology are carefully investigated and some illustrative examples are deeply discussed. Comparisons with the corresponding results obtained from homogeneous materials are made.Alberto CarpinteriMarco Paggimarco.paggi@imtlucca.it2013-11-25T10:15:57Z2014-10-09T09:20:26Zhttp://eprints.imtlucca.it/id/eprint/1937This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/19372013-11-25T10:15:57ZSnap-back instability in micro-structured composites and its connection with superplasticityInstability phenomena occurring in the microstructure of micro-structured composites are numerically investigated. To this aim, an interface constitutive law is proposed to describe both decohesion and contact at bi-material interfaces. These formulations are implemented in the FE code FEAP. Then, by applying dimensional analysis, the nondimensional parameters governing the macroscopic response of the composite are identified. According to this model, transverse debonding with respect to the fiber direction is simulated and the transition from snap-back instability in case of coarse fiber diameters, to a stable mechanical response for finer reinforcements is quantified. These results provide a possible quantitative explanation to the role played by the size of the reinforcement on the instability phenomena experimentally observed during superplastic deformation.Alberto CarpinteriMarco Paggimarco.paggi@imtlucca.itGiorgio Zavarise2013-11-25T10:04:08Z2014-10-09T09:20:26Zhttp://eprints.imtlucca.it/id/eprint/1936This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/19362013-11-25T10:04:08ZSize-scale effects on the friction coefficient An overview of the classical friction laws holding at the macro-scale and the new developments at the nano-level are proposed. Furthermore, two opposite phenomena are addressed: the former concerning the apparent weakness of the San Andreas fault, the latter regarding the strong frictional behavior which appears at the nano-scale. An interpretation of these size effects on the friction coefficient is attempted making use of the renormalization group procedure which allows to explain the frictional phenomena over all the scales. Alberto CarpinteriMarco Paggimarco.paggi@imtlucca.it2013-11-25T09:57:50Z2014-10-09T09:20:26Zhttp://eprints.imtlucca.it/id/eprint/1935This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/19352013-11-25T09:57:50ZInterface mechanical problems in heterogeneous materialsThe simplified assumption of material homogeneity underlying many problems of structural
mechanics is very often far from the complex reality we have to cope with. Junctions and
interfaces between di®erent materials must typically sustain mechanical and thermo-elastic
stresses without failure. Consequently, they exert an important and sometimes controlling
influence on the overall performance of the material. Therefore, current attempts in materials
engineering to increase the strength and ductility of materials require a full appreciation of
material interfaces, their properties and characterization.
Since interface problems are one of the main concern in civil, mechanical and electronic
engineering, as well as in biomechanics and in materials science, this research field is characterized
by multidisciplinary aspects. New concepts in engineering the material microstructure
mark the beginning of a paradigm shift in the way we think about materials and structures.
Due to recent advances in material processing, material and structural design considerations
are moving toward a full integration.
With this respect, it is evident that a proper modeling of the mechanical behavior of
interfaces at di®erent length scales is an outstanding point. The possibility of controlling the
mechanical behavior of the material over all the scales by tailoring interfaces clearly emerges
as one of the new challenges of the scientific community.
This thesis aims at giving a reasonably complete overview of the most relevant mathematical
and numerical techniques that can be applied to solve interface mechanical problems
in heterogeneous materials. With this objective in mind, the connections between the wide
literature of Linear Elastic and nonlinear Fracture Mechanics and Contact Mechanics are
deeply investigated and emphasized.
Novel features of this work include: (1) theoretical and numerical characterization of
stress-singularities arising at multi-material interfaces in 2D linear elastic problems; (2) numerical
and experimental study of brittle and fatigue crack growth in multi-layered materials;
(3) definition of a unified interface constitutive law for the study of decohesion and contact
problems at bi-material interfaces; and (4) interpretation of size-scale e®ects in new advanced
composite materials, such as the prediction of the critical grain sizes for the activation of
the superplastic behavior in fine grained composites and for the inversion of the Hall-Petch
relationship at the nano-scale.Marco Paggimarco.paggi@imtlucca.it2013-11-22T12:07:24Z2014-10-09T09:20:26Zhttp://eprints.imtlucca.it/id/eprint/1933This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/19332013-11-22T12:07:24ZCyclic Micro-slip and Energy Dissipation on Elastic Rough InterfacesA generalized approach is proposed, following the Mindlin and Deresiewicz procedure, to study
the cyclic behavior of surfaces in contact under a small oscillating tangential force. In order to
make the procedure straightforward and as general as possible, a non-dimensional formulation,
based only on the normal contact load-displacement curve, has been provided. It turns out that the
non-dimensional behavior under normal or tangential loading, as well as the energy dissipation
involved in cyclic loading, strongly depends on the exponent
α . This exponent can be calculated
explicitly in the case of profiles described by mathematical expressions (e.g. cylinders and
spheres), or can be determined from best fitting of experimental or numerical data (e.g. from
ICARUS simulations).
The larger is the exponent
α , the larger is the energy dissipated in small amplitude (partialslip)
tangential cycles.
Moreover, a comparison has been provided, without any claims of completeness, among some
of the theoretical models for the tangential interaction of rough surfaces available in the literature.
The calculation of the exponent α allows us to show the influence of different statistical
distribution assumptions of surface heights on the hysteretic energy dissipation.
Finally, the stick-slip behavior of rough surfaces subjected to oscillating loads has been
interpreted in terms of an analogy with the shake-down phenomenon described by the theory of
plasticity.Mauro Borri BrunettoStefano InvernizziMarco Paggimarco.paggi@imtlucca.itAlberto Carpinteri2013-11-22T11:53:51Z2014-10-09T09:20:26Zhttp://eprints.imtlucca.it/id/eprint/1932This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/19322013-11-22T11:53:51ZDelamination in FRP-strengthened structures: acoustic emission monitoring and numerical modelingA case study concerning both numerical modeling and in-situ monitoring of a retrofitted RC beam
with non-rectangular cross-section is presented. Before retrofitting, non-destructive techniques,
such as pull-out and impact tests, were used to estimate the mechanical parameters of concrete. At
the same time, a long-term monitoring with the Acoustic Emission (AE) technique was carried out
in order to investigate on creep effects and microcracking phenomena. Then, after a complete
removal of the overload and retrofitting with FRP sheets, an in-situ loading test was performed. At
that stage, the AE technique was again profitably used for the analysis of the cracking progression
leading to FRP debonding. A numerical model of the structure is then proposed in the framework
of the FE discretization with mechanical parameters estimated according to an inverse analysis on
the monitored mechanical behavior of the structure before retrofitting. According to this model, it
is clearly demonstrated that, when the flexural inertia of the retrofitted beam is considerably
higher than that of the unrepaired beam, snap-back instabilities can take place. Finally,
considering the self-similarity between the acoustic emission phenomenon and seismicity, an
analogy between the snap-back instability of the FRP delamination and that occurring during fault
growth is proposed.Giuseppe LacidognaMarco Paggimarco.paggi@imtlucca.itAlberto Carpinteri2013-11-22T11:19:24Z2014-10-09T09:20:26Zhttp://eprints.imtlucca.it/id/eprint/1931This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/19312013-11-22T11:19:24ZMulti-material junctions with functionally graded materialsComposites frequently involve situations where nonhomogeneous materials are either present
naturally, or used intentionally to attain a required mechanical performance. Starting from Bogy
(1968), bi- and multi-material junctions between different homogeneous materials have been
characterized from the stress-singularity point of view. In these studies, the material parameters
were assumed to be constant inside each material region and an abrupt discontinuity of the elastic
properties at the interfaces was allowed.
More recently, another class of materials, conventionally referred to as functionally graded
materials (FGMs), has been proposed, which involves materials whose elastic properties vary
continuously. When two materials are joined together, an abrupt discontinuity of the elastic
parameters, which is usually assumed for analytical purposes, does not exist in reality. On the
contrary, materials in the proximity of the interface possess continuous, rapidly varying elastic
moduli (Eischen (1987), Paulino (2002)).
In this paper the problem of stress-singularity due to multi-material junctions composed of
angularly nonhomogeneous elastic wedges in plane elasticity is addressed. For this new type of
grading the governing equation for the Airy stress function is derived and, by applying the
eigenfunction expansion method, a fourth order ODE with nonconstant coefficients for the
eigenequation is obtained. The solution to this ODE permits to formulate an eigenvalue problem
similar to that valid for material junctions between homogenous different materials. Moreover, it
is mathematically demonstrated that the angular grading influences the order of the stresssingularity.
The potentials of the use of this new class of materials in joining technology are
carefully investigated and some illustrative examples involving three-material junctions are deeply
discussed. ComparisonsMarco Paggimarco.paggi@imtlucca.itAlberto Carpinteri2013-11-22T11:04:09Z2014-10-09T09:20:26Zhttp://eprints.imtlucca.it/id/eprint/1930This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/19302013-11-22T11:04:09ZSoftening and snap-back instability in superplastic deformationThe mechanical behavior of micro-structured composites has been experimentally and theoretically proven to be strongly dependent on the size of the reinforcement. In other words,
keeping constant the reinforcement volumetric fraction and the mechanical properties of the constituent materials, size effects on the mechanical response are observed by varying the diameter of the inclusion. From the technological point of view, an important example where this
size effect is noticed is represented by superplasticity (Langdon, 1995). Instability phenomena occurring in the microstructure of micro-structured composites are
numerically investigated in this paper. To this aim, an interface constitutive law is proposed to
describe both decohesion and contact at bi-material interfaces. These formulations are
implemented in the FE code FEAP. Then, by applying dimensional analysis (Carpinteri, 1989),
the nondimensional parameters governing the macroscopic response of the composite are
identified. According to this model, transverse debonding with respect to the fiber/particle
direction is simulated and the transition from snap-back instability in case of coarse inclusion
diameters to a stable mechanical response for finer reinforcement is quantified. These results
provide a possible quantitative explanation to the role played by the size of the reinforcement on
the instability phenomena experimentally observed during superplastic deformation.Marco Paggimarco.paggi@imtlucca.itGiorgio ZavariseAlberto Carpinteri2013-11-22T10:24:43Z2014-10-09T09:20:26Zhttp://eprints.imtlucca.it/id/eprint/1929This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/19292013-11-22T10:24:43ZAcoustic emission monitoring and numerical modelling of a FRP-strengthened concrete structureAlberto CarpinteriGiuseppe LacidognaMarco Paggimarco.paggi@imtlucca.itNicola Pugno2013-11-22T10:10:05Z2014-10-09T09:20:26Zhttp://eprints.imtlucca.it/id/eprint/1928This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/19282013-11-22T10:10:05ZInfluence of the intermediate material on the singular stress field in tri-material junctionsAccording to the mathematical formalism of the eigenfunction expansion method, the problem of stress-singularities arising from multi-material junctions is addressed. The wedges are composed of isotropic homogeneous materials and are in a condition of plane stress or strain. The order of the stress-singularity is provided for tri-material junctions, paying special attention to the role played by Mode-I and Mode-II deformation. The effect of cracks inside either the softer or the stiffer material is also investigated. Numerical results can be profitably used for establishing optimum material configurations.Alberto CarpinteriMarco Paggimarco.paggi@imtlucca.it2013-11-22T09:59:13Z2014-10-09T09:20:26Zhttp://eprints.imtlucca.it/id/eprint/1927This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/19272013-11-22T09:59:13ZTheoretical and numerical investigation on internal instability phenomena in composite materialsInstability phenomena occurring in the microstructure of composite materials are investigated. To this aim, a complete description of the mechanical behavior of bi-material interfaces in composite materials requires the definition of both a cohesive law involving damage for the debonding stage, and a contact model during the closure of the interface. Both formulations are herein presented and implemented in the FE code FEAP. Numerical examples showing the transition from a snap-back instability to a stable mechanical response are presented.Alberto CarpinteriMarco Paggimarco.paggi@imtlucca.itGiorgio Zavarise2012-09-26T13:42:59Z2013-03-07T12:56:25Zhttp://eprints.imtlucca.it/id/eprint/1383This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/13832012-09-26T13:42:59ZVerifying parameterized protocols by transforming stratified logic programsWe propose a method for the specification and the automated verification of temporal properties of parameterized protocols. Our method is based on logic programming and program transformation. We specify the properties of parameterized protocols by using an extension of stratified logic programs. This extension allows premises of
clauses to contain first order formulas over arrays of parameterized length. A property of a given protocol is proved by applying suitable unfold/fold transformations to the specifiation of that protocol.We demonstrate our
method by proving that the parameterized Peterson's protocol among N processes, for any N ≥ 2, ensures the mutual exclusion property.Alberto PettorossiMaurizio ProiettiValerio Sennivalerio.senni@imtlucca.it2011-12-06T11:36:57Z2011-12-06T11:36:57Zhttp://eprints.imtlucca.it/id/eprint/1037This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/10372011-12-06T11:36:57ZNeural network model-based paper machine marginal cost curvesIn this paper we present a methodology for developing paper machine marginal cost curves, which include variable material and energy costs, fixed costs and overhead costs. The methodology is based on the radial basis function (RBF) neural network architecture and takes into account the complex interactions between the different mill departments. The outcome of the proposed method is the calculation of marginal costs for different paper machine production rates and different grades. The resulting cost curves can be used to take optimal decisions regarding paper machine loadings and optimize production allocation.Panagiotis Patrinospanagiotis.patrinos@imtlucca.itHaralambos SarimveisTh RetsinaS.R RutherfordAlex Alexandridis2011-12-06T11:03:54Z2011-12-06T11:03:54Zhttp://eprints.imtlucca.it/id/eprint/1036This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/10362011-12-06T11:03:54ZOptimal production scheduling for dairy industriesIn this work, a complete two-level framework for use in food and in particular dairy industries is proposed. The specific characteristics of the dairy industry have been taken into consideration, in terms of the behavior of food sales over time and the special requirements in the production phase. At the scheduling level, an MILP (Mixed Integer Linear Programming) model of the system was developed, using a continuous representation of time.Philip DoganisHaralambos SarimveisAlex AlexandridisPanagiotis Patrinospanagiotis.patrinos@imtlucca.it2011-12-06T10:51:35Z2011-12-06T10:51:35Zhttp://eprints.imtlucca.it/id/eprint/1035This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/10352011-12-06T10:51:35ZAn RBF based neuro-dynamic approach for the control of stochastic dynamic systemsThis paper presents a neuro-dynamic programming methodology for the control of markov decision processes. The proposed method can be considered as a variant of the optimistic policy iteration, where radial basis function (RBF) networks are employed as a compact representation of the cost-to-go function and the ॕ-LSPE is used for policy evaluation. We also emphasize the reformulation of the Bellman equation around the post-decision state in order to circumvent the calculation of the expectation. The proposed algorithm is applied to a retailer-inventory management problem.Panagiotis Patrinospanagiotis.patrinos@imtlucca.itHaralambos Sarimveis2011-12-05T11:40:26Z2011-12-05T11:40:26Zhttp://eprints.imtlucca.it/id/eprint/1027This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/10272011-12-05T11:40:26ZA two-stage evolutionary algorithm for variable selection in the development of RBF neural network modelsIn many modeling problems that are based on input–output data, information about a plethora of variables is available. In these cases, the proper selection of explanatory variables is very critical for the success of the produced model, since it eliminates noisy variables and possible correlations, reduces the size of the model and accomplishes more accurate predictions. Many variable selection procedures have been proposed in the literature, but most of them consider only linear models. In this work, we present a novel methodology for variable selection in nonlinear modeling, which combines the advantages of several artificial intelligence technologies. More specifically, the Radial Basis Function (RBF) neural network architecture serves as the nonlinear modeling tool, by exploiting the simplicity of its topology and the fast fuzzy means training algorithm. The proper variables are selected in two stages using a multi-objective optimization approach: in the first stage, a specially designed genetic algorithm minimizes the prediction error over a monitoring data set, while in the second stage a simulated annealing technique aims at the reduction of the number of explanatory variables. The efficiency of the proposed method is illustrated through its application to a number of benchmark problems.Alex AlexandridisPanagiotis Patrinospanagiotis.patrinos@imtlucca.itHaralambos SarimveisGeorge Tsekouras2011-11-22T13:39:08Z2011-12-20T12:00:25Zhttp://eprints.imtlucca.it/id/eprint/1018This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/10182011-11-22T13:39:08ZAction planning for graph transition systemsGraphs are suitable modeling formalisms for software and hardware systems involving aspects such as communication,
object orientation, concurrency, mobility and distribution. State spaces of such systems can be represented by graph transition systems, which are basically transition systems whose states and transitions represent graphs and graph morphisms. In this paper, we propose the modeling of graph transition systems in PDDL and the application of heuristic search planning for their analysis. We consider different heuristics and present experimental results.Stefan EdelkampShahid JabbarAlberto Lluch-Lafuentealberto.lluch@imtlucca.it2011-08-11T13:53:47Z2013-03-05T15:48:48Zhttp://eprints.imtlucca.it/id/eprint/810This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/8102011-08-11T13:53:47ZOn designing DNA databases for the storage and retrieval of digital signalsIn this paper we propose a procedure for the storage and retrieval of digital signals utilizing DNA. Digital signals are encoded in DNA sequences that satisfy among other constraints the Noise Tolerance Constraint (NTC) that we have previously introduced. NTC takes into account the presence of noise in digital signals by exploiting the annealing between non-perfect complementary sequences. We discuss various issues arising from the development of DNA-based database solutions (i) in vitro (in test tubes, or other materials) for short-term storage and (ii) in vivo (inside organisms) for long-term storage. We discuss the benefits and drawbacks of each scheme and its effects on the codeword design problem and performance. We also propose a new way of constructing the database elements such that a short-term database can be converted into a long term one and vice versa without the need for a re-synthesis. The latter improves efficiency and reduces the cost of a long-term database.Sotirios A. Tsaftarissotirios.tsaftaris@imtlucca.itAggelos K. Katsaggelos2011-08-11T13:47:12Z2013-03-05T15:49:00Zhttp://eprints.imtlucca.it/id/eprint/809This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/8092011-08-11T13:47:12ZA new codeword design algorithm for DNA based storage and retrieval of digital signalsSotirios A. Tsaftarissotirios.tsaftaris@imtlucca.itAggelos K. Katsaggelos2011-08-10T13:39:35Z2013-03-05T15:48:37Zhttp://eprints.imtlucca.it/id/eprint/791This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/7912011-08-10T13:39:35ZIn silico estimation of annealing specificity of query searches in DNA databasesWe consider DNA implementations of databases for digital signals with retrieval and mining capabilities. Digital signals are encoded in DNA sequences and retrieved through annealing between query DNA primers and data carrying DNA target sequences. The hybridization between query and target can be non-specific containing multiple mismatches thus implementing similarity-based searches. In this paper we examine theoretically and by simulation the efficiency of such a system by estimating the concentrations of query-target duplex formations at equilibrium. A coupled kinetic model is used to estimate the concentrations. We offer a derivation that results in an equation that is guaranteed to have a solution and can be easily and accurately solved computationally with bi-section root-finding methods. Finally, we also provide an approximate solution at dilute query concentrations that results in a closed form expression. This expression is used to improve the speed of the bi-section algorithm and also to find a closed form expression for the specificity ratios.Sotirios A. Tsaftarissotirios.tsaftaris@imtlucca.itVassily HatzimanikatiAggelos K. Katsaggelos2011-07-27T08:47:30Z2011-08-04T07:29:08Zhttp://eprints.imtlucca.it/id/eprint/522This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/5222011-07-27T08:47:30ZExplicit hybrid optimal control of direct injection stratified charge enginesThis paper illustrates the application of hybrid
modeling and receding horizon optimal control techniques
to the problem of air-to-fuel ratio and torque management
in advanced technology gasoline direct injection stratified
charge (DISC) engines. A DISC engine represents an example
of a constrained hybrid system, because it can operate
in two discrete modes (stratified and homogeneous) and
because the mode-dependent constraints on the air-to-fuel
ratio and on the spark timing need to be enforced. The paper
extends the prior work by the authors [1] and reports the
development of an explicit controller which implements the
optimal solution using piecewise affine functions of the state, thereby avoiding the need for on-line optimization. Strategies to simplify the explicit controller by reducing the number of regions in its characterization are discussed.Nicolò GiorgettiAlberto Bemporadalberto.bemporad@imtlucca.itIlya KolmanovskyDavor Hrovat2011-07-27T08:47:28Z2011-08-05T13:53:02Zhttp://eprints.imtlucca.it/id/eprint/533This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/5332011-07-27T08:47:28ZA decomposition algorithm for feedback min-max model predictive controlAn algorithm for solving feedback min-max model predictive control for discrete time uncertain linear systems with constraints is presented in the paper. The algorithm solves the corresponding multi-stage min-max linear optimization problem. It is based on applying recursively a decomposition technique to solve the min-max problem via a sequence of low complexity linear programs. It is proved that the algorithm converges to the optimal solution in finite time. Simulation results are provided to compare the proposed algorithm with other approaches. David Muñoz de la PeñaAlberto Bemporadalberto.bemporad@imtlucca.itTeodoro Alamo2011-07-27T08:47:26Z2011-08-05T13:52:41Zhttp://eprints.imtlucca.it/id/eprint/534This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/5342011-07-27T08:47:26ZStochastic programming applied to model predictive controlMany robust model predictive control (MPC) schemes are based on min-max optimization, that is, the future control input trajectory is chosen as the one which minimizes the performance due to the worst disturbance realization. In this paper we take a different route to solve MPC problems under uncertainty. Disturbances are modelled as random variables and the expected value of the performance index is minimized. The MPC scheme that can be solved using Stochastic Programming (SP), for which several efficient solution techniques are available. We show that this formulation guarantees robust constraint fulfillment and that the expected value of the optimum cost function of the closed loop system decreases at each time step. David Muñoz de la PeñaAlberto Bemporadalberto.bemporad@imtlucca.itTeodoro Alamo2011-07-27T08:47:24Z2011-08-05T13:52:14Zhttp://eprints.imtlucca.it/id/eprint/526This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/5262011-07-27T08:47:24ZInfinity norms as Lyapunov functions for model predictive control of constrained PWA systemsIn this paper we develop a priori stabilization conditions for infinity norm based hybrid MPC in the terminal cost and constraint set fashion. Closed-loop stability is achieved using infinity norm inequalities that guarantee that the value function corresponding to the MPC cost is a Lyapunov function of the controlled system. We show that Lyapunov asymptotic stability can be achieved even though the MPC value function may be discontinuous. One of the advantages of this hybrid MPC scheme is that the terminal constraint set can be directly obtained as a sublevel set of the calculated terminal cost, which is also a local piecewise linear Lyapunov function. This yields a new method to obtain positively invariant sets for PWA systems. Mircea LazarW.P.M.H. HeemelsSiep WeilandAlberto Bemporadalberto.bemporad@imtlucca.itOctavian Pastravanu2011-07-27T08:47:22Z2011-08-05T13:51:39Zhttp://eprints.imtlucca.it/id/eprint/530This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/5302011-07-27T08:47:22ZOn the stability and robustness of non-smooth nonlinear MPCThis paper considers discrete-time nonlinear, possibly discontinuous, systems in closed-loop with Model Predictive
Controllers (MPC). The aim of the paper is to provide a priori sufficient conditions for asymptotic stability in
the Lyapunov sense and robust stability, while allowing for both the system dynamics and the value function of the MPC cost (the usual candidate Lyapunov function in MPC) to be discontinuous functions of the state. The motivation for this work lies in the recent development of MPC for hybrid systems, which are inherently discontinuous and nonlinear systems. As an application of the general theory, it is shown that Lyapunov stability is achieved in hybrid MPC. For a particular class of piecewise affine systems, a modified MPC set-up is proposed, which is proven to be robust to small additive disturbances via an input-to-state stability argument.Mircea LazarW.P.M.H. HeemelsAlberto Bemporadalberto.bemporad@imtlucca.itSiep Weiland2011-07-27T08:45:21Z2011-08-04T07:29:07Zhttp://eprints.imtlucca.it/id/eprint/529This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/5292011-07-27T08:45:21ZPassivity analysis and passification of discrete-time hybrid systemsThis paper proposes several (sufficient) criteria based on the numerical solution of systems of linear matrix inequalities (LMIs) for proving the passivity of discrete-time hybrid systems in piecewise affine form, and for the synthesis of switched linear control laws that enforce passivity.Alberto Bemporadalberto.bemporad@imtlucca.itGianni BianchiniFilippo BrogiFederico Barbagli2011-07-27T08:45:16Z2011-08-05T13:48:46Zhttp://eprints.imtlucca.it/id/eprint/528This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/5282011-07-27T08:45:16ZOn the stability of quadratic forms based model predictive control of constrained PWA systemsIn this paper we investigate the stability of discrete-time PWA systems in closed-loop with quadratic cost based Model Predictive Controllers (MPC) and we derive a priori sufficient conditions for Lyapunov asymptotic stability.
We prove that Lyapunov stability can be achieved for the
closed-loop system even though the considered Lyapunov
function and the system dynamics may be discontinuous.
The stabilization conditions are derived using a terminal
cost and constraint set method. An S-procedure technique
is employed to reduce conservativeness of the stabilization
conditions and a linear matrix inequalities set-up is developed in order to calculate the terminal cost. A new algorithm for computing piecewise polyhedral positively invariant sets for PWA systems is also presented. In this manner, the on-line optimization problem associated with MPC leads to a mixed integer quadratic programming problem, which can be solved by standard optimization tools.Mircea LazarW.P.M.H. HeemelsSiep WeilandAlberto Bemporadalberto.bemporad@imtlucca.it2011-07-27T08:45:13Z2016-04-06T10:27:19Zhttp://eprints.imtlucca.it/id/eprint/523This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/5232011-07-27T08:45:13ZHybrid model predictive control application towards optimal semi-active suspensionThe optimal control problem of a quartercar semi-active suspension has been studied in the past.
Considering that a quarter-car semi-active suspension can
either be modeled as a linear system with state dependent
constraint on control (of actuator force) input, or a bilinear system with a control (of variable damping coefficient) saturation, the seemingly simple problem poses several interesting questions and challenges. Does the optimal control law derived from the corresponding un-constrained system, i.e. “clipped-optimal”, remain optimal for the constrained case? If the optimal control law of the constrained system does deviate from its un-constrained counter-part, how different are they? What is the structure of the optimal control law? In this paper, we attempt to answer some of the above questions by utilizing the recent development in model predictive control (MPC) of hybrid dynamical systems. The constrained quarter-car semi-active suspension is modeled as a switching affine system, where the switching is determined
by the activation of passivity constraints, force saturation, and maximum power dissipation limits. Theoretically, over an infinite prediction horizon the MPC controller corresponds to the exact optimal controller. The performance of different finite-horizon hybrid MPC controllers is tested in simulation using mixed-integer quadratic programming.
Then, for short-horizon MPC controllers, we derive the
explicit optimal control law and show that the optimal
control is piecewise affine in state. In particular, we show
that for horizon equal to one the explicit MPC control law
corresponds to clipped LQR. We will compare the derived
optimal control law to various semi-active control laws in
the literature including the well-known “clipped-optimal”.
We will evaluate their corresponding performances for both
a deterministic shock input case and a stochastic random
disturbances case through simulations.Nicolò GiorgettiAlberto Bemporadalberto.bemporad@imtlucca.itH. E. TsengDavor Hrovat2011-07-27T08:45:11Z2011-08-04T07:29:07Zhttp://eprints.imtlucca.it/id/eprint/453This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4532011-07-27T08:45:11ZA bounded-error approach to piecewise affine system identificationThis paper proposes a three-stage procedure for parametric identification of piecewise affine autoregressive exogenous (PWARX) models. The first stage simultaneously classifies the data points and estimates the number of submodels and the corresponding parameters by solving the partition into a minimum number of feasible subsystems (MIN PFS) problem for a suitable set of linear complementary inequalities derived from data. Second, a refinement procedure reduces misclassifications and improves parameter estimates. The third stage determines a polyhedral partition of the regressor set via two-class or multiclass linear separation techniques. As a main feature, the algorithm imposes that the identification error is bounded by a quantity δ. Such a bound is a useful tuning parameter to trade off between quality of fit and model complexity. The performance of the proposed PWA system identification procedure is demonstrated via numerical examples and on experimental data from an electronic component placement process in a pick-and-place machine.Alberto Bemporadalberto.bemporad@imtlucca.itAndrea GarulliSimone PaolettiAntonio Vicino2011-07-27T08:45:09Z2011-08-05T13:46:22Zhttp://eprints.imtlucca.it/id/eprint/452This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4522011-07-27T08:45:09ZDynamic programming for constrained optimal control of discrete-time linear hybrid systemsIn this paper we study the solution to optimal control problems for constrained discrete-time linear hybrid systems based on quadratic or linear performance criteria. The aim of the paper is twofold. First, we give basic theoretical results on the structure of the optimal state-feedback solution and of the value function. Second, we describe how the state-feedback optimal control law can be constructed by combining multiparametric programming and dynamic programming.Francesco BorrelliMato BaoticAlberto Bemporadalberto.bemporad@imtlucca.itManfred Morari2011-07-27T08:45:06Z2011-08-05T13:45:04Zhttp://eprints.imtlucca.it/id/eprint/532This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/5322011-07-27T08:45:06ZBounded model checking of hybrid dynamical systemsBounded model checking (BMC) has recently emerged as a very powerful methodology for the verification of purely discrete systems. Given a horizon of interest, bounded model checking verifies whether all finite-horizon trajectories satisfy a temporal logic formula by first translating the problem to a large satisfiability SAT-problem and then relying on extremely powerful state-of-the art SAT-solvers for a counterexample or a ertification of safety. In this paper we consider the problem of bounded model checking for a general class of discrete-time hybrid systems. Critical to our approach is the abstraction of continuous trajectories under discrete observations with a purely discrete system that captures the same discrete sequences. Bounded model checking can then be applied to the purely discrete, abstracted system. The performance of our approach is illustrated by verifying temporal properties of a hybrid model of an electronic height controller.Nicolò GiorgettiGeorge J. PappasAlberto Bemporadalberto.bemporad@imtlucca.it2011-07-27T08:45:04Z2014-03-05T13:44:04Zhttp://eprints.imtlucca.it/id/eprint/536This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/5362011-07-27T08:45:04ZEvent-driven optimal control of integral continuous-time hybrid automataThis paper proposes an event-driven optimal control trategy for hybrid systems composed of continuous-time integral dynamics with inputs and of Anite state machines triggered by endgenous and exogenous events. Endogenous events are caused by continuous states or continuous inputs crossing certain linear thresholds or by the elapse of time intervals, while exogenous events are forced by changes of binary and continuous inputs. The advantages of the roposed strategy are the reduction of the amount of computation required to solve optimal control problems, and the reduction of approximation errors typical of discrete-time approaches. We examine several performance objectives and constraints that lead to mixed-integerlinear or quadratic optimization problems and we exemplify the approach on a simple example.Alberto Bemporadalberto.bemporad@imtlucca.itStefano Di CairanoJorge Júlvez2011-07-27T08:45:02Z2011-08-05T13:50:39Zhttp://eprints.imtlucca.it/id/eprint/531This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/5312011-07-27T08:45:02ZModel predictive control of hybrid systems with applications to supply chain managementHybrid systems are dynamical systems whose behavior is determined by the interaction of continuous and discrete dynamics. Such systems arise in many real contexts, including automotive systems, chemical processes, communication networks, and supply chain management. A supply chain, whose goal is to transform ideas and raw materials into delivered products and services, is an example of a heterogeneous interconnection between continuous dynamics (inventory levels, material flows, etc.) and discrete dynamics (connection graphs, precedences, priorities, etc.). In general, in order to maximize a certain benefit or minimize certain costs, we have to optimally control all the heterogeneous components of the hybrid system. Model predictive control (MPC) is a well-known technique used in industry to (sub)optimally control dynamical processes, and is usually based on linear models.
This paper presents an overview of MPC techniques for hybrid systems. After giving a brief introduction to hybrid system models, model predictive control, and standard computation techniques, the paper summarizes recent results in using symbolic techniques and event-based formulations that exploit the particular structure of the hybrid process to come up with improved numerical computation schemes. The
concepts are illustrated through application examples in centralized management of supply chains.Alberto Bemporadalberto.bemporad@imtlucca.itStefano Di CairanoNicolò Giorgetti2011-07-27T08:44:59Z2011-08-04T07:29:07Zhttp://eprints.imtlucca.it/id/eprint/503This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/5032011-07-27T08:44:59ZOptimal control of discrete hybrid stochastic automataThis paper focuses on hybrid systems whose discrete state transitions depend on both deterministic and stochastic events. For such systems, after introducing a suitable hybrid model called Discrete Hybrid Stochastic Automaton (DHSA), different finite-time optimal control approaches are examined: (1) Stochastic Hybrid Optimal Control (SHOC), that “optimistically” determines the trajectory providing the best trade off between the tracking performance and the probability that stochastic events realize as expected, under specified chance constraints; (2) Robust Hybrid Optimal Control (RHOC) that, in addition, less optimistically, ensures that the system remains within a specified safety region for all possible realizations of stochastic events. Sufficient conditions for the asymptotic convergence of the state vector are given for receding-horizon implementations of the above schemes. The proposed approaches are exemplified on a simple benchmark problem in production system management. Alberto Bemporadalberto.bemporad@imtlucca.itStefano Di Cairano2011-07-27T08:44:57Z2011-08-04T07:29:07Zhttp://eprints.imtlucca.it/id/eprint/535This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/5352011-07-27T08:44:57ZPassivity analysis of discrete-time hybrid systems using piecewise polynomial storage functionsThis paper proposes some sufficient criteria based on the computation of polynomial and piecewise polynomial storage functions for checking passivity of discrete-time hybrid systems in piecewise affine or piecewise polynomial form. The computation of such storage functions is performed by means of convex optimization techniques via the sum of squares decomposition of multivariate polynomials.Alberto Bemporadalberto.bemporad@imtlucca.itGianni BianchiniFilippo BrogiGraziano Chesi2011-06-06T13:31:20Z2011-07-11T14:36:25Zhttp://eprints.imtlucca.it/id/eprint/309This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3092011-06-06T13:31:20ZMobile Distributed Programming in X-KlaimNetwork-aware computing has called for new programming languages that exploit the mobility paradigm as a basic interaction mechanism. In this paper we present X-Klaim, an experimental programming language specifically designed to program distributed systems composed of several components interacting through multiple distributed tuple spaces and mobile code. The language consists of a set of coordination primitives inspired by Linda, a set of operators for building processes borrowed from process algebras and a few classical constructs for sequential programming. X-Klaim naturally supports programming with explicit localities; these are first-class data that can be manipulated like any other data, and coordination primitives that permit controlling interactions among located processes. Via a series of examples, we show that many mobile code programming paradigms can be naturally implemented by means of the considered language.
Lorenzo BettiniRocco De Nicolar.denicola@imtlucca.it2011-06-06T12:46:30Z2011-07-11T14:36:25Zhttp://eprints.imtlucca.it/id/eprint/306This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3062011-06-06T12:46:30ZLanguages and Process Calculi for Network Aware Programming - Short Summary -We describe motivations and background behind the design of Klaim, a process description language that has proved to be suitable for describing a wide range of applications distributed over wide area networks with agents and code mobility. We argue that a drawback of Klaim is that it is neither a programming language, nor a process calculus. We then outline the two research directions we have recently pursued. On the one hand we have evolved Klaim to a full-fledged language for highly distributed mobile programming. On the other hand we have distilled the language to a number of simple calculi that we have used to define new semantic theories and equivalences and to test the impact of new operators for network aware programming. Rocco De Nicolar.denicola@imtlucca.it2011-06-06T12:42:54Z2011-07-11T14:36:25Zhttp://eprints.imtlucca.it/id/eprint/303This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3032011-06-06T12:42:54ZA Flexible and Modular Framework for Implementing Infrastructures for Global ComputingWe present a Java software framework for building infrastructures to support the development of applications for systems where mobility and network awareness are key issues. The framework is particularly useful to develop run-time support for languages oriented towards global computing. It enables platform designers to customize communication protocols and network architectures and guarantees transparency of name management and code mobility in distributed environments. The key features are illustrated by means of a couple of simple case studies. Lorenzo BettiniRocco De Nicolar.denicola@imtlucca.itDaniele FalassiMarc LacosteMichele Loreti2011-06-06T09:56:52Z2014-01-15T10:24:01Zhttp://eprints.imtlucca.it/id/eprint/302This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3022011-06-06T09:56:52ZA Process Calculus for QoS-Aware ApplicationsThe definition of suitable abstractions and models for identifying, understanding and managing Quality of Service (QoS) constraints is a challenging issue of the Service Oriented Computing paradigm. In this paper we introduce a process calculus where QoS attributes are first class objects. We identify a minimal set of primitives that allow capturing in an abstract way the ability to control and coordinate services in presence of QoS constraints. Rocco De Nicolar.denicola@imtlucca.itGianLuigi FerrariUgo MontanariRosario PuglieseEmilio Tuosto2011-06-03T14:57:15Z2011-07-11T14:36:25Zhttp://eprints.imtlucca.it/id/eprint/308This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3082011-06-03T14:57:15ZFormal modeling and quantitative analysis of KLAIM-based mobile systemsKLAIM is an experimental language designed for modeling and programming distributed systems composed of mobile components where distribution awareness and dynamic system architecture configuration are key issues. In this paper we propose STOCKLAIM, a STOchastic extension of cKLAIM, the core subset of KLAIM. cKLAIM includes process distribution, process mobility, and asynchronous communication. The extension makes it possible to integrate the modeling of quantitative aspects of mobile systems--- e.g. performance---with the functional specification of such systems. We present a formal operational semantics of STOcKLAIM, which associates a labeled transition system to each STOcKLAIM network and a translation to Continuous Time Markov Chains for quantitative analysis. We also show how STOcKLAIM can be used by means of a simple example, i.e. the modeling of the spreading of a virus.Rocco De Nicolar.denicola@imtlucca.itDiego LatellaMieke Massink2011-05-27T13:30:28Z2011-07-11T14:36:25Zhttp://eprints.imtlucca.it/id/eprint/301This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3012011-05-27T13:30:28ZGlobal Computing in a Dynamic Network of Tuple SpacesWe present a calculus inspired by Klaim whose main features are: explicit process distribution and node interconnections, remote operations, process mobility and asynchronous communication through distributed tuple spaces. We first introduce a basic language where connections are reliable and immutable; then, we enrich it with two more advanced features for global computing, i.e. failures and dynamically evolving connections. In each setting, we use our formalisms to specify some non-trivial global computing applications and exploit the semantic theory based on an observational equivalence to equationally establish properties of the considered case-studies.Rocco De Nicolar.denicola@imtlucca.itDaniele GorlaRosario Pugliese2011-05-27T12:47:58Z2011-07-11T14:36:25Zhttp://eprints.imtlucca.it/id/eprint/304This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3042011-05-27T12:47:58ZPattern Matching over a Dynamic Network of Tuple SpacesIn this paper, we present recent work carried on μ Klaim, a core calculus that retains most of the features of Klaim: explicit process distribution, remote operations, process mobility and asynchronous communication via distributed tuple spaces. Communication in μ Klaim is based on a simple form of pattern matching that enables withdrawal from shared data spaces of matching tuples and binds the matched variables within the continuation process. Pattern matching is orthogonal to the underlying computational paradigm of μ Klaim, but affects its expressive power. After presenting the basic pattern matching mechanism, inherited from Klaim, we discuss a number of variants that are easy to implement and test, by means of simple examples, the expressive power of the resulting variants of the language.
Rocco De Nicolar.denicola@imtlucca.itDaniele GorlaRosario Pugliese2011-05-25T12:14:27Z2011-07-11T14:36:25Zhttp://eprints.imtlucca.it/id/eprint/307This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3072011-05-25T12:14:27ZSemantic Subtyping for the p-CalculusSubtyping relations for the π-calculus are usually defined in a syntactic way, by means of structural rules. We propose a semantic characterisation of channel types and use it to derive a subtyping relation. The type system we consider includes read-only and write-only channel types, as well as Boolean combinations of types. A set-theoretic interpretation of types is provided, in which Boolean combinations are interpreted as the corresponding set-theoretic operations. Subtyping is defined as inclusion of the interpretations. We prove the decidability of the subtyping relation and sketch the subtyping algorithm. In order to fully exploit the type system, we define a variant of the π-calculus where communication is subjected to pattern matching that performs dynamic typecase.Giuseppe CastagnaRocco De Nicolar.denicola@imtlucca.itDaniele Varacca2011-05-25T12:02:56Z2011-07-11T14:36:25Zhttp://eprints.imtlucca.it/id/eprint/305This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3052011-05-25T12:02:56ZBasic Observables for a Calculus for Global ComputingWe introduce a foundational language for modelling applications over global computers whose interconnection structure can be explicitly manipulated. Together with process distribution, mobility, remote operations and asynchronous communication through distributed data spaces, the language provides constructs for explicitly modelling inter-node connections and for dynamically establishing and removing them. For the proposed language, we define natural notions of extensional observations and study their closure under operational reductions and/or language contexts to obtain barbed congruence and may testing equivalence. For such equivalences, we provide alternative characterizations in terms of a labelled bisimulation and a trace equivalence that can be used for actual proofs.Rocco De Nicolar.denicola@imtlucca.itDaniele GorlaRosario Pugliese2011-05-24T09:09:12Z2014-10-07T14:54:12Zhttp://eprints.imtlucca.it/id/eprint/311This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3112011-05-24T09:09:12ZOn the Expressive Power of Klaim-based CalculiIn this work, we study the expressive power of variants of Klaim, an experimental language with programming primitives for global computing that combines the process algebra approach with the coordination-oriented one. Klaim has proved to be suitable for programming a wide range of distributed applications with agents and code mobility, and has been implemented on the top of a runtime system based on Java. The expressivity of its constructs is tested by distilling from it some (more and more foundational) calculi and studying the encoding of each of the considered languages into a simpler one. An encoding of the asynchronous [pi]-calculus into one of these calculi is also presented.Rocco De Nicolar.denicola@imtlucca.itDaniele GorlaRosario Pugliese2011-05-24T09:03:36Z2011-07-11T14:36:25Zhttp://eprints.imtlucca.it/id/eprint/310This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3102011-05-24T09:03:36ZTypes in concurrencyRocco De Nicolar.denicola@imtlucca.itDavide Sangiorgi2011-03-24T11:00:40Z2015-02-11T14:37:46Zhttp://eprints.imtlucca.it/id/eprint/166This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/1662011-03-24T11:00:40ZQuantitative mu-calculus and CTL defined over constraint semiringsModel checking and temporal logics are boolean. The answer to the model checking question does a system satisfy a property? is either true or false, and properties expressed in temporal logics are defined over boolean propositions. While this classic approach is enough to specify and verify boolean temporal properties, it does not allow to reason about quantitative aspects of systems. Some quantitative extensions of temporal logics has been already proposed, especially in the context of probabilistic systems. They allow to answer questions like with which probability does a system satisfy a property?
We present a generalization of two well-known temporal logics: CTL and the [mu]-calculus. Both extensions are defined over c-semirings, an algebraic structure that captures quantitative aspects like quality of service or soft constraints. Basically, a c-semiring consists of a domain, an additive operation and a multiplicative operation, which satisfy some properties. We present the semantics of the extended logics over transition systems, where a formula is interpreted as a mapping from the set of states to the domain of the c-semiring, and show that the usual connection between CTL and [mu]-calculus does not hold in general. In addition, we reason about the complexity of computing the logics and illustrate some applications of our framework, including boolean model checking.Alberto Lluch-Lafuentealberto.lluch@imtlucca.itUgo Montanari2011-03-24T10:41:56Z2014-10-07T14:51:25Zhttp://eprints.imtlucca.it/id/eprint/165This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/1652011-03-24T10:41:56ZQuantitative mu-calculus and CTL Based on Constraint SemiringsModel checking and temporal logics are boolean. The answer to the model checking question does a system satisfy a property? is either true or false, and properties expressed in temporal logics are defined over boolean propositions. While this classic approach is enough to specify and verify boolean temporal properties, it does not allow to reason about quantitative aspects of systems. Some quantitative extensions of temporal logics has been already proposed, especially in the context of probabilistic systems. They allow to answer questions like with which probability does a system satisfy a property?
We present a generalization of two well-known temporal logics: CTL and the [mu]-calculus. Both extensions are defined over c-semirings, an algebraic structure that captures many problems and that has been proposed as a general framework for soft constraint satisfaction problems (CSP). Basically, a c-semiring consists of a domain, an additive operation and a multiplicative operation, which satisfy some properties. We present the semantics of the extended logics over transition systems, where a formula is interpreted as a mapping from the set of states to the domain of the c-semiring, and show that the usual connection between CTL and [mu]-calculus does not hold in general. In addition, we reason about the feasibility of computing the logics and illustrate some applications of our framework, including boolean model checking.Alberto Lluch-Lafuentealberto.lluch@imtlucca.itUgo Montanari2011-03-24T10:30:42Z2011-07-11T14:34:35Zhttp://eprints.imtlucca.it/id/eprint/164This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/1642011-03-24T10:30:42ZUsing Linear Temporal Model Checking for Goal-Oriented Policy Refinement FrameworksPolicy refinement is meant to derive lower-level policies from higher-level ones so that these more specific policies are better suited for use in different execution environments. Although it has been recognized as crucial, it has received relatively little attention. We present a policy refinement framework grounded in goal-elaboration methodologies and reactive systems analysis. Through linear-time model checking, we obtain system trace executions aimed at fulfilling lower-level goals refined with the KAOS goal-elaboration method. From system executions, we abstract managed entities, conditions and actions to encode the refined policies. We present our framework and provide a refinement scenario applied to the DiffServ QoS management domain.Javier Rubio-LoyolaJoan SerratParis FlegkasGeorge PavlouAlberto Lluch-Lafuentealberto.lluch@imtlucca.it2011-03-24T10:18:31Z2011-07-11T14:34:35Zhttp://eprints.imtlucca.it/id/eprint/163This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/1632011-03-24T10:18:31ZCost-Algebraic Heuristic SearchHeuristic search is used to efficiently solve the single-node
shortest path problem in weighted graphs. In practice, however,
one is not only interested in finding a short path, but
an optimal path, according to a certain cost notion. We propose
an algebraic formalism that captures many cost notions,
like typical Quality of Service attributes. We thus generalize
A*, the popular heuristic search algorithm, for solving
optimal-path problem. The paper provides an answer to a
fundamental question for AI search, namely to which general
notion of cost, heuristic search algorithms can be applied. We
proof correctness of the algorithms and provide experimental
results that validate the feasibility of the approach.Stefan EdelkampShahid JabbarAlberto Lluch-Lafuentealberto.lluch@imtlucca.it2011-03-08T10:56:15Z2011-07-11T14:33:43Zhttp://eprints.imtlucca.it/id/eprint/179This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/1792011-03-08T10:56:15ZA Compositional Coalgebraic Model of Monadic Fusion CalculusWe propose a compositional coalgebraic semantics of the Fusion calculus of Parrow and Victor in the version with explicit fusions by Gardner and Wischik. We follow a recent approach developed by the same authors and previously applied to the pi-calculus for lifting calculi with structural axioms to bialgebraic models. In our model, the unique morphism to the final bialgebra induces a bisimilarity relation which coincides with hyperequivalence and which is a congruence with respect to the operations. Interesting enough, the explicit fusion approach allows to exploit for the Fusion calculus essentially the same algebraic structure used for the pi-calculus. Maria Grazia Buscemim.buscemi@imtlucca.itUgo Montanari2011-03-01T09:27:17Z2011-07-11T14:33:43Zhttp://eprints.imtlucca.it/id/eprint/128This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/1282011-03-01T09:27:17ZA Method for Symbolic Analysis of Security ProtocolsIn security protocols, message exchange between the intruder and honest participants induces a form of state explosion which makes protocol models infinite. We propose a general method for automatic analysis of security protocols based on the notion of frame, essentially a rewrite system plus a set of distinguished terms called messages. Frames are intended to model generic crypto-systems. Based on frames, we introduce a process language akin to Abadi and Fournet's applied pi. For this language, we define a symbolic operational semantics that relies on unification and provides finite and effective protocol models. Next, we give a method to carry out trace analysis directly on the symbolic model. We spell out a regularity condition on the underlying frame, which guarantees completeness of our method for the considered class of properties, including secrecy and various forms of authentication. We show how to instantiate our method to some of the most common crypto-systems, including shared- and public-key encryption, hashing and Diffie–Hellman key exchange.Michele BorealeMaria Grazia Buscemim.buscemi@imtlucca.it2011-03-01T08:48:14Z2011-07-11T14:33:43Zhttp://eprints.imtlucca.it/id/eprint/127This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/1272011-03-01T08:48:14ZA General Name Binding MechanismWe study fusion and binding mechanisms in name passing
process calculi. To this purpose, we introduce the U-Calculus, a process
calculus with no I/O polarities and a unique form of binding. The latter
can be used both to control the scope of fusions and to handle new name
generation. This is achieved by means of a simple form of typing: each
bound name x is annotated with a set of exceptions, that is names that
cannot be fused to x. The new calculus is proven to be more expressive
than pi-calculus and Fusion calculus separately. In U-Calculus, the syntactic
nesting of name binders has a semantic meaning, which cannot be
overcome by the ordering of name extrusions at runtime. Thanks to this
mixture of static and dynamic ordering of names, U-Calculus admits a
form of labelled bisimulation which is a congruence. This property yields
a substantial improvement with respect to previous proposals by the
same authors aimed at unifying the above two languages. The additional
expressiveness of U-Calculus is also explored by providing a uniform encoding
of mixed guarded choice into the choice-free sub-calculus.Michele BorealeMaria Grazia Buscemim.buscemi@imtlucca.itUgo Montanari