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Giudizio immediato sullo stato di degrado dei ponti in c.a. basato su indagini low-cost
Get PDFThe structural engineer is often involved to express an opinion on the state of efficiency of the existing structures.
This is partly because, in Italy, a large part of structures was built before the middle of the last century. Indeed, the 14th General Census of Population and Housing in 2001, released by Istat, that counted 12.774.131 buildings and 38.397 building complexes, for a total of 12.812.528 units, shows that 19,2% (2.150.259) was built before 1919, 12,3% between 1919 and 1945, 50,0% between 1946 and 1981; 11,5% from 1982 to 1991 and 7,0% since 1991.
In addition to building, the field of road infrastructure requires as well special attention. In recent years the efficiency of infrastructure has been questioned due to various phenomena such as the increase in traffic loads, increasing the speed of travel, the changes of the relevant legislation relating to safety standards.
The functionality of the bridges depends closely on a good inspection activities, and the lack of a proper and timely maintenance, entails an increase of the deterioration and therefore higher costs of repair.
The periodic assessment of the conditions of stability of infrastructures is part of the duties of the company and Agencies owners of the roads. They are therefore directly responsible for any damage suffered by road users in dependence of instability or collapse of the bridges.
There is therefore the need to assess the reliability of the infrastructure, with particular attention to those who, although they have far exceeded their threshold of useful life, are still in operation.
In recent years, many companies of management of road networks have turned their interest to the definition of systems of Bridge Management System (BMS).
BMS is the set of inspection, investigation, maintenance, repair of a group of bridges, organized according to priority, with the support of computer databases and algorithms officers. The state of conservation is characterized by assigning qualitative judgments. Some BMS provide for the detection of the extension and intensity of the defects, others associate to each element a qualitative index relative to the condition in which is each element. The bibliographic study, showed that no existing method considers the location of the damage within the element in which it manifests itself, although it a fundamental parameter for a correct diagnosis as closely related to the kinematic mechanism of collapse.
The goal of my research work has been to provide a useful decision support tool during the data analysis of inspection, identifying a mode of low-cost and immediate investigation, for concrete bridges, which achieves a reliable judgment on the static condition of the structure inspected.
It has been given special attention to concrete structures, the most widely used material in the field of civil construction. Forty years ago, it was presented as a material with low maintenance and almost unlimited duration. Quite different is the situation that presents itself today to the industry, it is remarkable the presence in Italy of reinforced concrete structures subjected to situations of instability for which you need to make thorough checks to assess their strength.
The process that we propose is based: on visual observation of the bridge and on the analysis of the data obtained by means of instrumental tests carried out on the material to be inspected. Assuming that to do a good structural diagnosis, we must find the right compromise between reliability and invasiveness, it has been chosen, as a primary investigation, non-destructive tests, ie the complex of tests and surveys that do not alter the material and do not require the destruction of the structure. In particular, among the various non-destructive techniques, I chose to use the rebound hammer and ultrasonic testing techniques.
In order to verify the reliability of non-destructive testing, it has been arranged a campaign of experimental investigation of a series of mixtures, packaged with concrete class different to be able
to evaluate a wide range of resistances. They were made a total of 100 cubic test pieces of side 15 cm. They were then subjected to non-destructive tests for the measurement of the ultrasonic velocity and the rebound number, and in the end they were subjected to a breaking test for the determination of the compressive strength. It was then studied the correlation between the non-destructive testing and compression testing. The classical approach for the study of the correlation is to calibrate the regression lines between the indirect properties and the material characteristics and constructional of interest. The proposed methodology is based instead on the use of neural networks, which is a simple and quick tool of correlation between the measured and the mechanical properties of the material. From this practical application it has been identified neural networks as a way to better predict the value of concrete strength investigated, starting from the use of the results obtained by the low-invasive investigations.
The proposed method of assessment can be summarized into two steps:
• Visual inspection: identification and classification of any degradations and failures on the structure, it must be targeted to the identification of critical points that present and guide the subsequent phases of diagnostic. During the visual inspection is to be assessed the condition of each structural element, identifying extension, intensity and localization of all types of defect present.
• Instrumental analysis: mechanical characterization of materials based on low-invasive investigations (NDT).
For each significant parameter is assigned a numeric value that will form the basis for the calculation of the function of judgment of the single element (Fe). Adding the evaluation carried out for every individual element that make up the bridge and comparing this value to the sum of the defects that may potentially occur in the observed structure, you obtain the function evaluation of the whole structure (Fs).
The parameters for the assessment of the condition of the structure are therefore:
• data observable during visual inspections; technical arguments made by experts about the static scheme of the structure from which flows the importance that can have the location of the defect within the element on which it appears,
• the results of instrumental tests carried out on the material constituting the bridge.
The innovative aspect of the proposal, compared to the existing methods, is the introduction of two factors by which you can evaluate the location of the damage (Li), and use the mechanical characterization of the material as a parameter of judgment (Ti).
In support of the calculation method I proposed the Evaluation Tables to be completed during the visual inspections to note down observations. In this way you can make it clear how, starting from what was found during the inspection, for each structural element, it was possible to issue the final judgment.
The applicability of the method was verified by means of application on three real structures. The first two are located in Pixina Manna (Pula) and the third structure is located a few kilometres far from the city of Cagliari.
Application examples show that the method is an important aid to the evaluation of the structure, providing a guide for the technician who must carry out the survey and directing a uniformity of opinion
Structure-based approaches applied to the study of pharmaceutical relevant targets
Get PDFComputer Aided Drug Design/Discovery methods became complementary to traditional and modern drug discovery approaches. Indeed CADD is useful to improve and speed up the detection and the optimization of bioactive molecules. The present study is focused on the application of structure-based approaches to the study of pharmaceutical relevant targets. The introduction provides a quick overview on the fundamentals of computational chemistry and structure-based methods, while in the successive chapters the main targets investigated through these methods are treated. In particular we focused our attention on Reverse Transcriptase of HIV-1, Monoamine oxidase B and VP35 of Ebola virus. The last chapter is dedicated to the validation of covalent docking performed with Autodock
Characterization of the Roman lines/strains of rats as a genetic model of psychiatric disorders: a behavioral and brain dialysis study
Get PDFState of the art Depressive disorders are fairly prevalent in the general population, with a higher rate in women compared to men, are disabling, since they can significantly impair psychosocial functioning, and are typically associated with high mortality due mainly to the high rate of suicides but also to the negative impact that depression has on the course of co-occurring illnesses. In addition, pharmacological and psychological antidepressant therapies in use have a limited efficacy and/or are associated with side effects that reduce the compliance in many patients. Although the etiology and pathogenesis of depression are poorly understood, it is most likely that the combination of genetics, early life adverse events, and ongoing stress may ultimately determine the individual vulnerability to stress-related disorders, such as depression. Therefore, the development and characterization of animal models of vulnerability and resistance to the effects of stress, including early life stress, is a major challenge for depression research.
One such model is represented by the Roman high- (RHA) and low-avoidance (RLA) lines/strains of rats, which are psychogenetically selected for, respectively, rapid versus extremely poor acquisition of active avoidance in a shuttle box. A large body of evidence indicates that a major reason for their divergent performance in this test is their different reactivity to stressful stimuli, that is, their coping style. Thus, when exposed to aversive stimuli, RLA rats display a reactive coping strategy, associated with a strong activation of the HPA axis; moreover, they display robust depressive-like behaviors in the forced swim test (FST) that are normalized by the subacute administration of antidepressants. In contrast, compared with their RLA counterparts, RHA rats display a proactive coping strategy in the face of aversive conditions, associated with higher baseline levels of impulsivity, a more robust sensation/novelty seeking profile, a marked preference for, and intake of, natural and drug rewards along with a greater responsiveness of the mesolimbic dopaminergic system.Aims The behavioral and neurochemical traits that distinguish the two lines/strains suggest that RLA rats may represent a model of vulnerability to stress-induced depression, whereas RHA rats may model resistance to stress-induced depression-like behaviour.
To test this hypothesis, in the first study we evaluated the performance of RLA and RHA rats in the FST in response to chronic antidepressant treatments, since clinical evidence indicates that several weeks of treatment with antidepressant drugs are required to achieve an adequate therapeutic response.
Furthermore, one of the cardinal symptoms of depression observed in many patients is anhedonia, which is defined as the loss of interest in once enjoyable activities, including sexual activity. Accordingly, depressive episodes are frequently associated with sexual dysfunctions. In consideration of this clinical evidence, and given the well-established role of dopamine in sexual behavior, the second study was aimed at characterizing the sexual behavior of RHA and RLA rats and its correlation with the functional state of their mesolimbic dopaminergic system.
In keeping with the long-term consequences on mental health elicited by early-life adverse events, it has been observed that post weaning social isolation in rodents may lead to a later increment in the prevalence of anxiety/fear related behaviors. Thus, in the third study we evaluated the impact of post weaning isolation on the anxiety-related behaviors of inbred RHA and RLA rats in the Elevated Zero Maze, and in motility cages used to asssess locomotor activity in a new environment.
Results In study I we demonstrated that chronic treatments with low doses of antidepressants, that were ineffective when given subacutely, were able to decrease immobility and also to increase climbing (desipramine) or swimming (fluoxetine) in RLA rats. Conversely, neither subacute nor chronic antidepressant treatments affected the behavior of RHA rats in the FST.
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In addition, the results of study II showed that, compared with their RLA counterparts, RHA rats displayed higher levels of sexual motivation and a better copulatory performance, associated with a greater release of DA in the AcbSh. These line-related differences were attenuated but not abolished by sexual experience. Moreover, RLA rats were more responsive than their RHA counterparts to both, the facilitatory effect of apomorphine and the inhibitory effect of haloperidol on sexual behavior.
Finally, in study III we found that the isolation-rearing procedure significantly increased the level of anxiety of RHA-I rats in the EZM, as reflected by a smaller number of entries and a shorter time spent in the open space, associated with decreased head dipping, increased latency to enter in the open space, and reduced novelty-induced locomotor activation, whereas it failed to produce significant changes in the behavior of RLA-I rats.
Conclusions The results of these studies show that the Roman lines/strains of rats may represent a valid experimental approach to investigate the neural substrates and molecular mechanisms involved in the individual vulnerability and resistance to stress-induced depression, with the aim of identifying both, potential biomarkers for an early diagnosis of depression and potential molecular targets for novel antidepressant treatments. Moreover, the Roman lines/strains may be used to study the neurophysiology of the appetitive and consummatory aspects of sexual behaviour, in order to better understand the mechanisms underlying the psychological and pathological causes of sexual dysfunctions. Finally, the Roman rats may provide a useful model to identify the mechanisms whereby early-life adverse events interact with the genetic make up to induce psychiatric disorders in adulthood
Diritto alla salute e ICT: tra controllo della spesa e verifica di appropriatezza
Get PDFThis paper aims to analyze the state of the art of the application of new technologies in the healthcare industry and its use in the activity of appropriateness and cost control monitoring. All the reforms that have recently affected the health demonstrated the orientation of the legislator towards a rationalization of costs through more efficient use of available resources. This reorganization of the sector has been inevitably influenced by several factors such as the evolution of the concept of the right to health accepted nowadays as a financially affected right, the polycentric and multilevel nature of the health sector and the requirements to control the public spending that have strongly conditioned by obligations of supranational origin.
In this context, the ICT (Information Communications technologies) could have played a central role in enabling both a better management of the sector (through the ESF) and the creation of appropriate means of cost trend (using the NSIS).
However up to now, despite the current regulations, suitable systems have not been put in place to take advantage of all the opportunities provided by ICT tools in this area, as the outlined system is fragmented and inadequate to allow an effective and efficient check of the choices undertaken by the health system’s actors.
Throughout the report we will analyze some of the current ICT tools used in the health sector, highlighting the critical issues and identifying any remedial actions in order to get a greater functional use in accordance with the new requirements of control and monitoring
Ecological features, populations traits and conservation status of Helianthemum caput-felis along its distribution range
No full textUnderstanding factors limiting populations’ growth and persistence is crucial to evaluate the current conservation status and possible future management of plant populations. This Ph.D. thesis focussed on ecological constraints related to population trends and the conservation status of Helianthemum caput-felis Boiss., characterized by a highly fragmented areal isolated from the distribution centre. In particular, the specifics aims of the thesis were: (1) to analyse the distribution range, population size, the reproductive traits, the effect of human disturbance and identify the threats affecting the persistence of H. caput-felis in Sardinia following the IUCN regional protocol; (2) to investigate flowers and fruits phenology, ecological traits (geomorphology, substrate, slope and human trampling intensity) affecting reproductive outputs (as fruit and seed sets) and the presence of two ecological gradients along the entire European distribution range of the species; (3) to discover the population dynamics by the analyses of populations vital rates, both at global level than a local scale; (4) to evaluate the risk of extinction of H. caput-felis at global level, and then to assess the global conservation status of the populations, together with an accurate analysis of the global area of occupancy of the species, following the IUCN protocol.
The thesis results indicate relevant aspect regarding the ecology, population dynamics, distribution and conservation traits of the species.
In Sardinia, the species preferably grows in lowland areas with deep structured soil, due to the amount of water and resources available and morphological stability. H. caput-felis shows the highest reproductive output in garrigues, habitat that represents its ecologically optimum. The high seed production indicates that this is not a limiting factor for this plant, in contrast to seedling establishment, which represent its main critical stage. Surprisingly, in Sardinia, human trampling enhanced the plant size and the rate of fruits production, suggesting that reproductive plants of H. caput-felis are tolerant to direct damage, and probably benefit from the reduction of inter-specific and intra-specific competition.
Comparing the phenology and reproductive output along the entire European distribution range of this species over a two year temporal context indicate that the general phenological pattern of H. caput-felis was similar among Sardinian and Majorcan regions, whereas, in the eastern Iberian populations (the western part of the distribution range), the southern population (Cabo Roig) showed a higher inter-annual variability and an early flowering period. Those differences could be related to a longitudinal aridity gradient for this plant: the aridity decreases from western to eastern localities. Plants growing at the eastern edge of the distribution range (Sardinia) produce more viable fruits, fruits per plant and seeds per fruit than the other two regions, while plants growing in arid substrate (as in the sandy habitat of Sa Ràpita, Majorca) are the least productive, confirming that sandy substrate is negatively correlated with fruits production and viable fruits, as well as lowland geomorphology. Hence, these analyses underline that the Abundant Centre Model assumptions, by which reproductive traits should be higher at the centre of species distribution, is not confirmed for H. caput-felis, maybe because the central populations, represented by the largest distribution area along the Iberian’s coasts, appear strongly fragmented mainly by human disturbance.
Demographic traits of H. caput-felis population were analysed, by using demographic surveys, integrated by Matrix and Integral Projection Models (MPM and IPM, respectively). Plant performance and population dynamics were investigated in plants sampled along the comprehensive and representative part of the European distribution range in which the species occurs. The global population showed a general stability in the first year transition, after which it declined. This trend was probably due to the higher shrinkage of plants in the last year of study, which correlates negatively with reproductive traits, in agreement with the frequent increase in reproductive outputs with plant size. Despite this decline, stochastic population growth rate highlighted as H. caput-felis
population oscillated around the equilibrium. Elasticity analysis indicated the higher importance of large individuals and the determinant role of the survival-growth transitions for the population growth rate. Moreover, plants reached high generation times and mean long life span, which, with the limited seedling recruitment rate and the presence of a consistent seed bank, reflect patterns that are typical both of many long-lived plants and of calcareous rupicolous Mediterranean species. IPM methods were found to be more accurate than MPM to monitoring species with restricted range, as H. caput-felis.
At local level, the pattern of typical long-lived Mediterranean plants was also confirmed; in fact, populations were mainly composed from large individuals, characterized by slow growth. H. caput-felis showed vital rates and population dynamics varying among populations: the Sardinians’ seems to have greater equilibrium than Spanish populations. The high population growth rates of Moraira and Colònia de Sant Jordi were strongly influenced by the fecundity parameters. Plants growing in Moraira show a uniform shrinkage of individuals, probably due to a more intense fragmentation of the population. The different population dynamics observed among the analysed localities of H. caput-felis should be correlated to particular microclimate and ecological conditions, i.e. the high aridity of Cabo Roig and the sand substrate of Sa Ràpita, which probably affected the relationship among size and vital rates. On the contrary, H. caput-felis populations in demographic equilibrium, as the Sardinians’, could be locally adapted to ecological and microclimate conditions.
Finally, population dynamics models were applied to analyse the extinction risk and then assess the global conservation status of H. caput-felis, together with an accurate analysis of the global area of occupancy of the species, following the IUCN protocol. This research highlighted that H. caput-felis should be considered an Endangered (EN) plant at global level, according to the formula B2ab (ii,iii,iv,v) + E. H. caput-felis suffered a continuing decline in AOO, quality of its habitat, number of localities and number of reproductive plants. This decline rate was mainly due to the habitat loss and the expansion of infrastructures detected in the last decades. Hence, effective future conservation measures could be focussed on protecting the single localities where H. caput-felis grows, in order to avoid further species decline. In this contest, conservation efforts primarily aimed to protect established individuals (mature plants) against disturbances, as suggested for other long-lived species.
The results of this thesis gave new findings for the ecology and conservation of H. caput-felis, and demonstrate the importance to considerate both global than local level in demography and phenology studies
Centralised and decentralised control of active distribution systems: models, algorithms and applications.
Get PDFPower system were traditionally planned and designed by assuming unidirectional power flows from power stations to loads. Nowadays, several factors (e.g., liberalization of the electricity market, need of increased reliability, and environmental issues) lead to a situation where electricity is produced also downstream the transmission level. Connecting generators to the distribution networks could provide several benefits to the whole system, but also technical and safety problems that must be faced. On the other hand, the loads are changing: new loads like electric vehicles and electric pumps are appearing in the network and they are going to modify the electricity consumption; while traditional loads are designed in order to be more efficient, but with additional functions or special features that require more energy.
For all these reasons, since 2005, the interest on Smart Grid (electricity network that can intelligently integrate the actions of all users connected to it – generators, consumers – in order to efficiently deliver sustainable, economic and secure electricity supplies) increased.
In this framework different techniques to control, operate and thereby integrate distributed energy resources into the network have been analysed and developed. The first technique designed is a centralised control, characterised by a central controller (Distribution Management System) that gathers information like the measures of the main electric parameters, energy price and indicates to DERs (Active Loads, Generators, Energy Storage) the optimal set points minimizing the system cost, subject to technical and economical constraints. The second technique developed is a decentralised control using Multi Agent Systems (MAS). This type of control has been designed and developed for the direct control of active demand and plug-in electric vehicles, managed by the Aggregator, entrusted by the end users to change their consumption habits according to their needs. Moreover, the proposed decentralised MAS, with the active participation of small consumers in the electricity system, support the integration of the Electric Vehicles in the LV distribution network and reduce its harmful impact on voltage regulation.
The techniques and the algorithms proposed by the author are analysed and applied in representative Italian Distribution networks, by taking into account the development of the distribution system according to the load profile evolution, providing several examples to underline the importance of the Active Management for deferring the reinforcement of the existing grid infrastructures, increasing the hosting capacity of the networ
New shape and texture descriptors for an improved germplasm characterization of the most representative Mediterranean vascular flora, by image analysis technology
Get PDFThe focus of this doctoral thesis concerned the application of Image
Analysis technique for an adequate definition of the seed morphocolorimetric
parameters, that represents an important diagnostic factor in the
plant taxonomy studies and consequently may be of great help for the
improvement of the management and the effective ex situ conservation in the
germplasm banks.
The first part of this study was related to the computer vision
fundamentals and statistical treatment of data. Based on the clear concept that
the discriminant ability of a classification system depends not only on the
intra-specific representativeness of taxa analyzed, but also on the quality and
quantity of the parameters measured and used to discriminate between groups
of belonging, a new set of recordable shape and texture variables was
introduced in a yet consolidated image analysis system, with the aim to
improve the performance of the classifiers. In the second part of this
dissertation some case studies are reported as applications of this innovative
technology, with the aim to prove its great usefulness for systematic
purposes. The results here presented confirmed that an extensive database of
morpho-colorimetric traits may be applied for taxonomy screening of species
groups, comparing with the current systematic, as well as with groupings
more recently revealed by genetic studies.
The morpho-colorimetric characterization of Cistus L. (Cistaceae)
seeds by image analysis was treated: a database of morphometric and
colorimetric data was carried out to statistically discriminate and identify
both at inter and intra-specific and populational level. The satisfactory discrimination performances reached agree with the results reported in the
previous papers on the same taxa, though, the improvement of the image
analysis system adopted, in which an overall of 138 seed features was
evaluated, allowed to reinforce the discrimination power also when the
morphometric variability within each group, such as in inter-population
groups, is extremely reduced. The taxonomical differentiation within the
Medicago L. sect. Dendrotelis (Fabaceae) was also described. The obtained
results confirmed the validity of the proposed method for the taxonomic
differentiation of Medicago at specific levels, and its identification capability
of regional and populational groups. Furthermore, the relationships among 79
taxa belonging to the Lavatera and Malva genera were tretated, in order to
contribute to their doubtful systematic treatment.
Finally, this innovative kind of identification system, which method
was specifically developed to identify wild seeds, and that requires only a
few seconds for scanning and measurement operations, proved to be a quick,
repeatable, reliable and non destructive method. It does not require any
chemical reagents, expensive analytical consumables or high priced physical
preparation of samples, hence it is a very cheap method. This precise and
accurate identification system it was only possible thanks to efficient and
useful cooperation between taxonomists and image analysis specialists. The
expert, practical experience in such different fields allowed the development
of a system so complex in its structure and so simple in the use. Indeed,
having a broad database of morpho-colorimetric seed features for an adequate
amount of families, genera and species would enable the identification of
taxa already present in the database. In this way, this innovative tool would
open new perspectives in plant taxonomy, but also offer the opportunity for
germplasm banks to make identifications in a standard, speedy way. In addition, the availability of morpho-colorimetric data should be
helpful for ecological and/or archeobotanical studies such as the prediction of
seed persistence in the soil
Parametric modeling of dependence of bivariate quantile regression residuals' signs
Get PDFIn this thesis, we propose a non-parametric method to study the dependence of the
quantiles of a multivariate response conditional on a set of covariates. We define a
statistic that measures the conditional probability of concordance of the signs of the
residuals of the conditional quantiles of each univariate response. The probability
of concordance is bounded from below by the value of largest possible negative
dependence and from above by that of largest possible positive dependence. The
value corresponding to the case of independence is contained in the interior of that
interval. We recommend two distinct regression methods to model the conditional
probability of concordance. The first is a logistic regression with a logit link modified.
The second one is a nonlinear regression method, where the outcome is modeled as
a polynomial function of the linear predictor. Both are conceived to constrain the
predicted probabilities to lie within the feasible range. The estimated probabilities
can be tested against the values of largest possible dependence and independence.
The method permits to capture important aspects of the dependence of multivariate
responses and assess possible effects of covariates on such dependence. We use data
on pulmonary disfunctions to illustrate the potential of the proposed method. We
suggest also graphical tools for a correct interpretation of results
Applications of low-rank approximation: complex networks and inverse problems
Get PDFThe use of low-rank approximation is crucial when one is interested in solving
problems of large dimension. In this case, the matrix with reduced rank can
be obtained starting from the singular value decomposition considering only
the largest components. This thesis describes how the use of the low-rank
approximation can be applied both in the analysis of complex networks and in
the solution of inverse problems.
In the first case, it will be explained how to identify the most important
nodes or how to determine the ease of traveling between them in large-scale
networks that arise in many applications. The use of low-rank approximation is
presented both for undirected and directed networks, whose adjacency matrices
are symmetric and nonsymmetric, respectively.
As a second application, we propose how to identify inhomogeneities in the
ground or the presence of conductive substances. This survey is addressed
with the aid of electromagnetic induction measurements taken with a ground
conductivity meter. Starting from electromagnetic data collected by this device,
the electrical conductivity profile of the soil is reconstructed with the aid of a
regularized damped Gauss{Newton method. The inversion method is based on
the low-rank approximation of the Jacobian of the function to be inverted
Consensus in multi-agent systems with time-delays
Get PDFDifferent consensus problems in multi-agent systems have been addressed in this thesis. They represent improvements with respect to the state of the art. In the first part of the thesis in luding Chapters 2, 3, and 4, the state of the art of the representation and stability analysis of consensus problems, time-delay systems, and sampled-data systems have been presented. Novel contributions have been illustrated in Chapters 5-8. Particularly, in Chapter 5 we reported the results of Zareh et al. (2013b), where we investigated the consensus problem for networks of agents with double integrator dynamics affected by time-delay in their coupling. We provided a stability result based on the Lyapunov-Krasovskii functional method and a numerical proc edure based on an LMI condition which depends only on the algebraic connectivity of the considered network topologies, thus reducing greatly the computational complexity of the procedure. Obviously, this result implies the existence of a minimum dwell time such that the proposed consensus protocol is stable for slow swit things between network topologies with suffient algebraic connectivity. Future work will involve actually computing such a dwell time by adopting a multiple Lyapunov function method and evaluating the worst case sider only delayed relative measurements instead of delayed absolute values of the neighbors' state variables. The results of Zareh et al. (2013a) were addressed in Chapter 6, in which a on- tinuous time version of a consensus on the average protocol for arbitrary strongly connected directed graphs is proposed and its convergence properties with respect to time delays in the local state update are characterized. The convergenc e properties of this algorithm depend upon a tuning parameter that an be made arbitrary small to prove stability of the networked system. Simulations have been presented to corroborate the theoretical results and show that the existenc e of a small time delay an a tually improve the algorithm performance. Future work will include an extension of the mathematical characterization of the proposed algorithm to consider possibly heterogeneous or time-varying delays. In Chapter 7 we proposed a PD-like consensus algorithm for a second-order multi- agent system where, at non-periodic sampling times, agents transmit to their neighbors information about their position and veloc ity, while each agent has a perfect knowledge of its own state at any time instant. Conditions have been given to prove onsensus to a ommon xed point, based on LMIs verification. Moreover, we also show how it is possible to evaluate an upper bound on the de ay rate of exponential convergence of stable modes. In Chapter 8, mainly based on our paper Zareh et al. (2014b), we considered the same problem as in Chapter 7. The main contribution consists in proving consensus to a common fixed point, based on LMIs verification, under the assumption that the network topology is not known and the only information is an upper bound on the connectivity. Two are the main directions of our future research in this framework. First, we want to compute analytically an upper bound on the value of the second largest eigenvalue of the weighted adjacency matrix that guarantees consensus, as a function of the other design parameters. Second, we plan to study the case where agents do not have a perfect knowledge of their own state