Fitting dynamic factor models to non-stationary time series

Factor modelling of a large time series panel has widely proven useful to reduce its cross-sectional dimensionality. This is done by explaining common co-movements in the panel through the existence of a small number of common components, up to some idiosyncratic behaviour of each individual series. To capture serial correlation in the common components, a dynamic structure is used as in traditional (uni- or multivariate) time series analysis of second order structure, i.e. allowing for infinite-length filtering of the factors via dynamic loadings. In this paper, motivated from economic data observed over long time periods which show smooth transitions over time in their covariance structure, we allow the dynamic structure of the factor model to be non-stationary over time, by proposing a deterministic time variation of its loadings. In this respect we generalise existing recent work on static factor models with time-varying loadings as well as the classical, i.e. stationary, dynamic approximate factor model. Motivated from the stationary case, we estimate the common components of our dynamic factor model by the eigenvectors of a consistent estimator of the now time-varying spectral density matrix of the underlying data-generating process. This can be seen as time-varying principal components approach in the frequency domain. We derive consistency of this estimator in a "double-asymptotic" framework of both cross-section and time dimension tending to infinity. A simulation study illustrates the performance of our estimators.econometrics;

Nondegenerate abnormality, controllability, and gap phenomena in optimal control with state constraints

In optimal control theory, infimum gap means that there is a gap between the infimum values of a given minimum problem and an extended problem, obtained by enlarging the set of original solutions and controls. The gap phenomenon is somewhat "dual" to the problem of the controllability of the original control system to an extended solution. In this paper we present sufficient conditions for the absence of an infimum gap and for controllability for a wide class of optimal control problems subject to endpoint and state constraints. These conditions are based on a nondegenerate version of the nonsmooth constrained maximum principle, expressed in terms of subdifferentials. In particular, under some new constraint qualification conditions, we prove that: (i) if an extended minimizer is a nondegenerate normal extremal, then no gap shows up; (ii) given an extended solution verifying the constraints, either it is a nondegenerate abnormal extremal, or the original system is controllable to it. An application to the impulsive extension of a free end-time, non-convex optimization problem with control-polynomial dynamics illustrates the results

Impulsive optimal control problems with time delays in the drift term

We introduce a notion of bounded variation solution for a new class of nonlinear control systems with ordinary and impulsive controls, in which the drift function depends not only on the state, but also on its past history, through a finite number of time delays. After proving the well posedness of such solutions and the continuity of the corresponding input output map with respect to suitable topologies, we establish necessary optimality conditions for an associated optimal control problem. The approach, which involves approximating the problem by a non impulsive optimal control problem with time delays and using Ekeland principle combined with a recent, nonsmooth version of the Maximum Principle for conventional delayed systems, allows us to deal with mild regularity assumptions and a general endpoint constraint

No Infimum Gap and Normality in Optimal Impulsive Control Under State Constraints

In this paper we consider an impulsive extension of an optimal control problem with unbounded controls, subject to endpoint and state constraints. We show that the existence of an extended-sense minimizer that is a normal extremal for a constrained Maximum Principle ensures that there is no gap between the infima of the original problem and of its extension. Furthermore, we translate such relation into verifiable sufficient conditions for normality in the form of constraint and endpoint qualifications. Links between existence of an infimum gap and normality in impulsive control have previously been explored for problems without state constraints. This paper establishes such links in the presence of state constraints and of an additional ordinary control, for locally Lipschitz continuous data

Stakeholder Oriented Analysis for Information Intensive Applications: A Case Study

We present an approach to Requirements Elicitation based on AWARE, a goal oriented technique conceived for Web applications. The approach integrates a goal-oriented analysis of the needs of each stakeholder class with a subsequent phase of function-oriented analysis. Goal-oriented analysis facilitates an active participation of users and, therefore, can be considered as a substantial step towards user acceptance of the system. Our approach introduces the use of predefined diagrams of user’s needs and confirmation/disconfirmation interviews, that easies and fastens user interaction. The approach was tested on an Information Intensive Application, namely a collaborative document management system for a fast growing Management Consulting organization. The system will support both marketing activities and consulting work on the whole life cycle of consulting projects. In our case study the goal-oriented approach actually encouraged active participation of future users in the dynamic and unstructured environment typical to a Management Consulting organization. The active user participation helped analyst to maximize the potential value supplied to each professional and to minimize the future effort required to use the system. The consulting organization is currently implementing the system and decided to adopt the approach also for their customers

New Therapeutic Strategies in the Treatment of Stomal Recurrence After Total Laryngectomy: Role of Immunotherapy

Objective: The aim of this study was to investigate the incidence of stoma recurrence and the therapeutic strategy outcomes in relation to survival that have been adopted over the past few decades using a monoclonal antibody, specifically nivolumab. Methods: This study included a total of 487 patients diagnosed with laryngeal carcinoma undergoing either a laryngectomy or salvage surgery after conservative interventions at the ENT Unit of Federico II University in Naples, Italy, between 2011 and 2021. Following a minimum 2.5-year follow-up and a maximum 21-year follow-up, the results revealed that only 38 patients suffered a stomal recurrence. Results: Despite various adopted treatment strategies, the literature reports lower patient survival rates. Following a total laryngectomy, stomal recurrence represents a therapeutic management challenge due to a poor prognosis for nearly every treated case. According to the literature, in fact, despite a low incidence (ie, 0.8–31.3%), the overall mortality rate increases from 77% to 100% after three years. Nevertheless, introducing immunotherapy into cancer treatment has resulted in an observable revolution in the treatment of different types of cancers over the years. Conclusion: In light of recorded data on survival following the use of the nivolumab, the case presented in this study allows a new perspective of successfully treating recurrences of squamous carcinoma of the head and neck. © The Author(s) 2022

Reacting to the Emergency by Opening Perspectives. Design-driven knit therapy as a adaptable tool to answer the change

When the COVID-19 emergency raised, the entire world -and small communities with it- had to stop, adapt, find ways to face the big ongoing challenge. The article reports the reaction and the changes undertaken with an ongoing project that was, in February 2020, experimenting, inside the hospital environment, the therapeutic effects of knitting on people with physical and psychological pathologies. The project, driven by scientific studies made in universities, hospitals and research centers worldwide, had the aim to bring the intervention of designers on the topic, to answer the emerged need to promote research in what is considered a low-investigated and high-promising field. Experimental pilot actions, designed and led by designers on-field, were going on when the emergency changed the scenario, limited the environment, shifted the eye on a new, wider target of healthy people, made knitting a tool to face new circumstances and improve everyday-life quality.Observing the newly emerged scenario and the spontaneous initiatives risen on the web (and on social media in particular) to help individuals in spending the forced time at home in meaningful ways, designers involved in the ongoing project identified in knitting an activity that could be beneficial on a psychological and physical level also for quarantined individuals. The project took a new perspective and evolved in the #IOLAVOROAMAGLIA (#IKNIT) social media campaign, linked to the globally spread #STAYHOME campaign, aimed at inviting people to remain home for preventing the diffusion of the infection, while proposing at the same time new solutions for positively living the emergency times. #IOLAVOROAMAGLIA was embraced by many users and it also became a weekly scheduled live virtual workshop, with a direct reference to the workshops in the hospital of XXXX, temporarily stopped during lockdown.The two projects, on-field and online, proved how knitting can be a meaningful solution not only for healthcare, but also for the daily life of people, both in normal times and in emergency situations.Moreover, the role of the designer and of a design driven approach proved to be fundamental, for the product and service creation, improvement and consolidation and for its communication for valorization and promotion