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In digital social networks, the filtering algorithms employed by the platform management to sieve the contents shared among the users can alter the social influence intensity. In this article, a Markov multiagent model of opinion dynamics is used to analyze possible opinion manipulation under apparently neutral interventions on the influence intensity. We consider a two-party election, whose voters, modeled as heterogeneous agents, are connected in a social network with an arbitrary topology. The equations describing the variance of the vote share, both in transient and steady state, are derived. The key is the solution of the second-order marginalization problem under the form of a numerically tractable characterization of pairwise joint probabilities of the voters’ opinions. In particular, these probabilities are computed by means of a Lyapunov-like matrix differential equation driven by first-order moments. This result is used to answer some important questions, like the possible nonmonotonic effect of the influence intensity on the vote volatility and the interplay of topology and individuals’ stubbornness to determine the electoral balance between two parties.

Despite progress in clinical care for patients with coronavirus disease 2019 (COVID-19)1, population-wide interventions are still crucial to manage the pandemic, which has been aggravated by the emergence of new, highly transmissible variants. In this study, we combined the SIDARTHE model2, which predicts the spread of SARS-CoV-2 infections, with a new data-based model that projects new cases onto casualties and healthcare system costs. Based on the Italian case study, we outline several scenarios: mass vaccination campaigns with different paces, different transmission rates due to new variants and different enforced countermeasures, including the alternation of opening and closure phases. Our results demonstrate that non-pharmaceutical interventions (NPIs) have a higher effect on the epidemic evolution than vaccination alone, advocating for the need to keep NPIs in place during the first phase of the vaccination campaign. Our model predicts that, from April 2021 to January 2022, in a scenario with no vaccine rollout and weak NPIs (R0= 1.27), as many as 298,000 deaths associated with COVID-19 could occur. However, fast vaccination rollouts could reduce mortality to as few as 51,000 deaths. Implementation of restrictive NPIs (R0= 0.9) could reduce COVID-19 deaths to 30,000 without vaccinating the population and to 18,000 with a fast rollout of vaccines. We also show that, if intermittent open–close strategies are adopted, implementing a closing phase first could reduce deaths (from 47,000 to 27,000 with slow vaccine rollout) and healthcare system costs, without substantive aggravation of socioeconomic losses.

This paper deals with the class of positive linear systems subject to Poisson jumps. The random jumps are described by an exponential distribution with mode-dependent parameter. Contrary to classical Markov Jump Linear Systems, no probabilistic information on the sequence of modes is assumed to be available. Mean stability of this class of systems is analyzed, showing that it is equivalent to stability under arbitrary switching of a suitably defined deterministic switching system. Sufficient conditions for mean stability are worked out by relying on common copositive (linear or quadratic) Lyapunov functions. Similar conditions are derived for designing a state-feedback control law guaranteeing closed-loop mean stability and positivity.

This paper deals with switched linear systems subject to time-varying delay. The main goal is to design state and output feedback switching strategies preserving closed-loop stability and a guaranteed H2or H∞performance. The switching strategies are based on a generalization of a recent extended version of the small gain theorem and do not require any assumption on the continuity of the delay and its time-variation rate. The key point to obtain the design conditions is the adoption of an equivalent switched linear system where the time-varying delay is modeled as a norm-bounded perturbation. Moreover, with this approach, it is possible to deal with sampled-data control systems. All conditions are formulated in terms of Lyapunov–Metzler inequalities, which allow the maximization of an upper bound on the time-delay preserving stability and guaranteed performance. Numerical examples are discussed in order to illustrate the effectiveness of the design approach.

The article focuses on the creation of the student-led organization Sexpression: UK in Great Britain to provide sex and relationship education in primary and secondary schools through partnership with local schools and youth clubs.

Dual switching linear systems are systems with piecewise linear dynamics governed by two distinct external switching signals. In this paper one switching signal is stochastic and modeled as a time-homogeneous Markov chain, and the second one is assumed to be a control signal taking values in a finite set. This situation arises, for instance, in multi-loop networked control systems (NCS) with limited transmission capacity and lossy communication channels, where the control variable is the scheduling signal and the stochastic switching accounts for packet dropout. The aim of this paper is to derive suitable switching strategies for dual switching linear systems, ensuring mean-square stability and attaining guaranteed bounds on ℋ2and ℋ∞performance indices. The relevant sufficient conditions are expressed in terms of feasibility of sets of coupled matrix inequalities. The application to a scheduling design problem in NCS's is also discussed.

This paper deals with the stabilization issue of switched linear systems with time-delays. Based on previous results related to switched linear systems with no time-delays and on the concept of piecewise quadratic Lyapunov-Krasovskii functionals, we solve the problem of searching output feedback switching laws ensuring stability. Our synthesis method is based on the solution of a set of matrix inequalities associated with the modes of the switched system.

This paper proposes a novel approach to address the H∞control problem of switched linear systems through the assignment of the switching law. Exploiting the relationship existing between H∞control problems and differential games, which has been analyzed in depth in the literature, we reformulate the original control problem as the solution of a Hamilton-Jacobi-Isaacs equation depending on the switching signal. The solution of such an equation is not trivial in general, but an effective numerical procedure is proposed to deal with it in the case of planar systems.

This paper deals with the notion of almost sure stability for linear stochastic systems whose dynamic matrix depends on an ergodic process. It is shown that such systems are exponentially almost surely stable if and only if their transition matrix is averagely contractive over a finite, yet unknown, time interval. In order to test this condition, an efficient computational procedure based on a Monte Carlo strategy is proposed. Moreover, an H8condition ensuring exponential almost sure stability is proven. The condition requires that the mean square value of the ergodic process is less than a constant involving the H8-norm of an appropriate transfer function. The applicability of the proposed methods is illustrated by means of a numerical example.

The paper deals with special classes of H∞ estimation problems, where the signal to be estimated coincides with the uncorrupted measured output. Explicit bounds on the difference between nominal and actual H∞ performance are obtained by means of elementary algebraic manipulations. These bounds are new in continuous-time filtering and discrete-time one-step ahead prediction. As for discrete-time filtering, the paper provides new proofs that are alternative to existing derivations based on the Krein spaces formalism. In particular, some remarkable H∞ robustness properties of Kalman filters and predictors are highlighted. The usefulness of these results for improving the estimator design under a mixed H2/H∞ viewpoint is also discussed. The dualization of the analysis allows one to evaluate guaranteed H∞ robustness bounds for state-feedback regulators of systems affected by actuator disturbances. Copyright © 2001 John Wiley & Sons, Ltd.

The paper deals with special classes of H∞estimation problems, where the signal to be estimated coincides with the uncorrupted measured output. Explicit bounds on the difference between nominal and actual H∞performance are obtained by means of elementary algebraic manipulations. These bounds are new in continuous‐time filtering and discrete‐time one‐step ahead prediction. As for discrete‐time filtering, the paper provides new proofs that are alternative to existing derivations based on the Krein spaces formalism. In particular, some remarkable H∞robustness properties of Kalman filters and predictors are highlighted. The usefulness of these results for improving the estimator design under a mixed H2/H∞viewpoint is also discussed. The dualization of the analysis allows one to evaluate guaranteed H∞robustness bounds for state‐feedback regulators of systems affected by actuator disturbances. Copyright © 2001 John Wiley & Sons, Ltd.

Wiskott-Aldrich syndrome (WAS) is an X-linked disorder characterized by congenital thrombocytopenia and progressive deterioration of the immune function. Dendritic cells (DC) are key effectorsin the induction of specific immunity and are highly specialized in antigen uptake and subsequent migration to draining lymph nodes. DC were generated in vitro from circulating monocytes from ten WAS patients characterized by a different disease score. Immature DC showed similar morphology and membrane phenotype, as compared to normal DC. In chemotaxis assay, immature DC had a reduced migration in response to MIP-1α/CCL3, but efficiently endocytosed the macromolecules FITC-dextran and FITC-albumin. Upon terminal differentiation with LPS or CD40 ligand, the acquisition of a mature surface phenotype was variably achieved among WAS patients, with increased expression of CD80, CD86 and DC-LAMP. In contrast, the expression of CD83 was usually low. A defective up-regulationof CD83 was also observed in the lymph node from one WAS patient, whose DC stained positively for DC-LAMP. Mature DC from all the patients tested, but one, significantly migrated in vitro in response to MIP-3β, a finding confirmed in vivo by the detection of HLA-DR/DC LAMP-positive cells in secondary lymphoid organs. When tested in MLR assays, both immature and mature WAS DC induced allogenic T cell proliferation in a manner comparable to control DC. Collectively these results suggest that, although many functional activities of WAS DC are essentially similar to normal DC, subtle and selective alterations of DC differentiation were also observed, with reduced migratory activity of immature DC and defective CD83 expression upon maturation.

The paper deals with H∞control of systems affected by actuator disturbances, and H∞filtering of signals buried in noise (Wiener filtering) . Explicit bounds on the difference between nominal and actual H∞performance are obtained by means of elementary algebraic manipulations. These bounds extend discrete-time results that were previously derived using Krein spaces formalism to continuous-time. In particular, some remarkable H∞robustness properties of the Kalman filter and the LQ regulator are highlighted.

The cement gland is a secreting organ located at the anterior end of the larva of anuran Amphibia. It is a highly conserved structure even if it has different shapes in the different species. The morphology and the histology of the cement glands of seven species are analysed: Xenopus laevis, Discoglossus sardus, Bufo bufo, Bufo viridis, Rana esculenta, Rana latastei and Hyla intermedia. XCG and XAG are genes specifically expressed in the cement gland of Xenopus laevis and can be used as markers to identify cement gland territory. By Northern analysis and whole mount 'in situ' hybridization, the expressions of these genes are tested in the studied species, the presence of homolog transcripts is detected in all the species, except Discoglossus sardus. Histological and molecular analysis show a substantial uniformity among the different types of adhesive organs. On the basis of the preliminary results obtained, some phylogenetic relations are inferred according to a recent phylogenetic tree based on molecular characters. The results seem to agree with the hypothesis that Pipi-dae, to which Xenopus laevis belongs, are nearer to Neobatrachia than to Archeobatrachia.

Adaptive filtering of a scalar signal corrupted by noise is considered. In particular, the signal to be estimated is given as a linear regression model depending on a drifting parameter. The mean-square and worst-case performances of the H8-adaptive filter are studied. Bounds for the mean-square performance are established on the basis of upper bounds for the solution of the relevant Riccati equation. As for the worst-case performance, it is shown that an H8-.filter designed with a certain value of the parameter ? ensures an easy-to-compute attenuation level less than ?.

The paper deals with the canonical decomposition of discrete-time linear systems based on the classical properties of reachability, controllability, observability and reconstructibility. First, a set of relationships between the structural subspaces is established and used to derive a general form of the discrete-lime duality principle. By means of these results, a sufficient condition for the existence of a canonical decomposition is worked out. Such a condition is also necessary if the attention is focused on decompositions based on the classical structural properties. Depending on the pair of properties considered, four different decompositions can be achieved. Finally, by making reference to controllability and reconstructibility a canonical decomposition is shown to exist for periodic systems. In general, non-reversible periodic systems admit no other decomposition but this one.

This paper deals with the problem of qualifying the class of linear dynamical systems which can be represented as time-varying ARMA models. It is proved that any r-step uniformly observable system admits an ARMA representation of order r and, conversey, an ARMA model of order r can be represented by means of an r-step observable system. Minimality of ARMA models is then discussed. It is shown that the ARMA representation of certain systems requires more parameters than the correspondent minimal state-space realization.

The monitoring and prediction of the evolution of software reliability, during the program debugging phase can be performed by means of suitable failure growth models. In this paper, a stochastic model for software reliability is proposed and applied to experimental data. The main feature of the model is that the so called fault exposure coefficient is allowed to vary linearly with the number of discovered failures. This implies that a number of different growth curves can be generated by the model so that a variety of different situations can be described. The model parameters are identified by resorting to the Maximum Likelihood approach, and approximated confidence intervals are evaluated by means of the Fisher information matrix.

It is known that the finite-horizon H8-filter exists provided that the solution of a suitable H8Difference Riccati Equation (DRE) exists and satisfies a ‘feasibility’ condition. In this paper, sufficient conditions ensuring feasibility and convergence to the steady-state stabilising solution are derived. In particular, convergence can be guaranteed if the initial condition ofthe DRE is not much greater than the stabilising solution. For a fixed value of the attenuation level ? the finite-horizon H8-filter may fail to converge to the steady-state stabilising filter. Hence, a strategy employing a time-varying attenuation level ?(t) is worked out so as to ensure both feasibility and convergence to the desired steady-state filter.

In this paper a robust controller for a four-wheel steering (4WS) vehicle is designed by using μ-synthesis techniques. Main goals of the design are the improvement of high-speed turning performance in terms of stability and sideslip reduction. Stability and performance robustness is achieved against variations of the cornering tire stiffness coefficients. Simulations with a nonlinear car steering model show the merits of the proposed control strategy, under μ-split braking maneuver and side wind gust disturbance.

The paper illustrates various techniques for the selection of weights in robust identification schemes based on a bank of RLS estimators with different forgetting factors. A simulation study shows the effectiveness of such an approach both in open-loop and closed-loop operation.

Motivated by the research on active control of helicopter vibrations, in this paper we present a novel dynamic model of the vibrations induced on the fuselage by the blades. The model provides a small-variation relationship between the swash-plate commands and the vertical force at the rotor hub. Based on data obtained from an Agusta Company simulator, the identified model consists of a time-invariant linear dynamic system complemented with periodically time-varying linear and algebraic blocks.

The design of robust predictors for discrete-time linear systems subject to norm-bounded parameter perturbations is considered. The proposed finite-horizon predictor minimizes an upper bound of the prediction error covariance and its computation calls for the solution of two difference Riccati equations. The existence and convergence over an infinite-horizon of the predictor applied to a time-invariant system with a given initial state covariance are also studied. The predictor is shown to converge to the stable steady-state optimal guaranteed-cost predictor whenever the initial state covariance is less than the antistabilizing solution of the Riccati equation of quadratic stability analysis.

The sign indefinite Differential Riccati Equation (ORE) arising in finite-horizon H∞filtering and control is analyzed. Differently from the standard sign definite DRE, the solution of the H∞DRE can have finite escape times also for nonnegative initial conditions. Moreover, reachability and observability are not sufficient to ensure convergence to the stabilizing solution. The paper provides easy-to-verify sufficient conditions guaranteeing boundedness and convergence.

The present study focuses on the changes of protein patterns that occur with age and on their maintenance across orthoclonal generations (i.e., lines that belong to the same clone and that differ with the age of their ancestors). About 500 individuals of the bdelloid rotifer Macrotrachela quadricornifera were cultivated and processed, and their protein phenotypes compared by a similarity test. The number of protein bands decreased with the age of the individuals. Young rotifers had the young protein pheno-type when born from young mothers, and the old protein pattern when born from aged ones. The age of their grandmother was irrelevant. On the basis of these results, bdelloid rotifers seemed to transmit to the offspring their biochemical phenotype modified by age and the modified phenotype could persist over the two generations considered. Thus, a truly evolutionarily ancient partheno-genetic taxon, such as Bdelloidea, apparently produces variable offspring by transmitting phenotypic variations induced by non-genetic factors.

An Independent Joint Control based force-position control strategy of industrial manipulators involved in a controlled sliding of the end effector on a plane surface is presented in this paper. The force control design model relies on a stiff contact model of the interaction, thus avoiding the need for (fictitious) contact stiffness parameters. The dynamic performances of the proposed control schemes have been tested by simulation, with reference to the industrial robot DEXTER.

Most work on micromixing within the last decade has considered stirred tank reactors. Here the core region of turbulent flow in a pipe is studied experimentally and theoretically. A neutralization as well as the azo coupling between 1-naphthol and diazotised sulphanilic acid were conducted in the core and, combined with a micromixing model, led to local rates of turbulent energy dissipation. These were compared with values available in the literature and determined from physical measurements. The chemically determined values were somewhat greater, possibly due to the radial movement of the reagents from the centre line and additional turbulence generated by the feed pipe. Nevertheless Eq. (11) should apply to micromixing in the core. Total average rates of energy dissipation greatly exceeded the turbulent rates in the core.

This paper deals with the computation of upper bounds for the state covariance matrix of discrete-time linear systems subject to stochastic excitation and additive time-varying uncertainty in the system dynamic matrix. Such upper bounds are obtained as the stabilizing solutions of suitable H ∞ -type Riccati equations. A necessary and sufficient condition for the existence of such solutions is given in terms of the H ∞ -norm of a suitable transfer function. As for the computation of the optimal bound, it is demonstrated that the bounds are a convex function of a scalar parameter, so that efficient numerical schemes can be worked out.

Stochastic linear systems subject to time-varying parameter uncertainties affecting both system dynamics and noise statistics are considered. A linear filter is used to estimate a linear combination of the states of the system. When the filter is given, the stabilizing solution of a suitable Riccati equation is shown to yield an upper bound for the covariance of the estimator error. The main problem addressed in the paper is the design of an 'optimal robust filter' that minimizes such a covariance bound. Necessary conditions are given for the existence of an optimal reduced-order robust filter as well as necessary and sufficient conditions for the full-order case. The computation of the optimal filter calls for the solution of a Riccati equation that generalizes the standard Riccati equation for the Kalman filtering problem. A numerical example is provided in which the new filter is compared with both the Kalman and H∞-filters.