Tuning of the functional beamforming resolution for wind tunnel measurements

Conventional Frequency Domain Beamforming (CB) is characterised by the frequency dependency of the mainlobe width and by the presence of sidelobes that limit its dynamic range. Functional Beamforming (FB) has been introduced with the aim to overcome these limitations, narrowing the mainlobe and reducing the sidelobe levels. This paper introduces a strategy to obtain a beamformer with a target mainlobe width that is constant over a desired frequency range. The idea is to properly adjust the Functional Beamforming order ν, frequency by frequency, to preserve the mainlobe width. A tuning procedure of the order ν is presented and applied to a typical wind tunnel setup. A detailed analysis of the dependency “order ν versus frequency” is discussed and a general formula describing this dependency is provided. Finally, the effectiveness of the proposed approach is shown both on simulated and experimental test case

Age-related relationships among peripheral B lymphocyte subpopulations

An immunological data-driven model is proposed, for age related changes in the network of relationships among cell quantities of eight peripheral B lymphocyte subpopulations, that is, cells exhibiting all combinations of three specific receptor clusters (CD27, CD23, CD5). The model is based on immunological data (quantities of cells exhibiting CD19, characterizing B lymphocytes) from about six thousands patients, having an age ranging between one day and ninety-five years, by means of a suitably combination of data analysis methods, such as piecewise linear regression models. With relaxed values for statistically significant models (coefficient p-values bounded by 0.05), we found a network holding for all ages, that likely represents the general assessment of adaptive immune system for healthy human beings. When statistical validation comes to be more restrictive, we found that some of these interactions are lost with aging, as widely observed in medical literature. Namely, interesting (inverse or directed) proportions are highlighted among mutual quantities of a partition of peripheral B lymphocytes

Policy Interpretation for Partially Observable Monte-Carlo Planning: A Rule-Based Approach

Partially Observable Monte-Carlo Planning (POMCP) is a powerful online algorithm that can generate online policies for large Partially Observable Markov Decision Processes. The lack of an explicit representation of the policy, however, hinders interpretability. In this work, we present a MAX-SMT based methodology to iteratively explore local properties of the policy. Our approach generates a compact and informative representation that describes the system under investigation

Identification of unexpected decisions in Partially Observable Monte Carlo Planning: a rule-based approach

Partially Observable Monte-Carlo Planning (POMCP) is a powerful online algorithm able to generate approximate policies for large Partially Observable Markov Decision Processes. The online nature of this method supports scalability by avoiding complete policy representation. The lack of an explicit representation however hinders interpretability. In this work, we propose a methodology based on Satisfiability Modulo Theory (SMT) for analyzing POMCP policies by inspecting their traces, namely sequences of belief-action-observation triplets generated by the algorithm. The proposed method explores local properties of policy behavior to identify unexpected decisions. We propose an iterative process of trace analysis consisting of three main steps, i) the definition of a question by means of a parametric logical formula describing (probabilistic) relationships between beliefs and actions, ii) the generation of an answer by computing the parameters of the logical formula that maximize the number of satisfied clauses (solving a MAX-SMTproblem), iii) the analysis of the generated logical formula and the related decision boundaries for identifying unexpected decisions made by POMCP with respect to the original question. We evaluate our approach on Tiger, a standard benchmark for POMDPs, and a real-world problem related to mobile robot navigation. Results show that the approach can exploit human knowledge on the domain, outperforming state-of-the-art anomaly detection methods in identifying unexpected decisions. An improvement of the Area Under Curve up to 47% has been achieved in our tests

The Time of Flight System of the AMS-02 Space Experiment

The Time-of-Flight (TOF) system of the AMS detector gives the fast trigger to the read out electronics and measures velocity, direction and charge of the crossing particles. The new version of the detector (called AMS-02) will be installed on the International Space Station on March 2004. The fringing field of the AMS-02 superconducting magnet is $1.0\div2.5$ kG where the photomultiplers (PM) are installed. In order to be able to operate with this residual field, a new type of PM was chosen and the mechanical design was constrained by requiring to minimize the angle between the magnetic field vector and the PM axis. Due to strong field and to the curved light guides, the time resolution will be $150\div180$ ps, while the new electronics will allow for a better charge measurement.Comment: 5 pages, 4 figures. Proc. of 7th Int. Conf. on Adv. Tech. and Part. Phys., 15-19 October 2001,Como (Italy

Quantum Plasmonics with multi-emitters: Application to adiabatic control

We construct mode-selective effective models describing the interaction of N quantum emitters (QEs) with the localised surface plasmon polaritons (LSPs) supported by a spherical metal nanoparticle (MNP) in an arbitrary geometric arrangement of the QEs. We develop a general formulation in which the field response in the presence of the nanosystem can be decomposed into orthogonal modes with the spherical symmetry as an example. We apply the model in the context of quantum information, investigating on the possibility of using the LSPs as mediators of an efficient control of population transfer between two QEs. We show that a Stimulated Raman Adiabatic Passage configuration allows such a transfer via a decoherence-free dark state when the QEs are located on the same side of the MNP and very closed to it, whereas the transfer is blocked when the emitters are positioned at the opposite sides of the MNP. We explain this blockade by the destructive superposition of all the interacting plasmonic modes

Explaining the influence of prior knowledge on POMCP policies

Partially Observable Monte Carlo Planning is a recently proposed online planning algorithm which makes use of Monte Carlo Tree Search to solve Partially Observable Monte Carlo Decision Processes. This solver is very successful because of its capability to scale to large uncertain environments, a very important property for current real-world planning problems. In this work we propose three main contributions related to POMCP usage and interpretability. First, we introduce a new planning problem related to mobile robot collision avoidance in paths with uncertain segment difficulties, and we show how POMCP performance in this context can take advantage of prior knowledge about segment difficulty relationships. This problem has direct real-world applications, such as, safety management in industrial environments where human-robot interaction is a crucial issue. Then, we present an experimental analysis about the relationships between prior knowledge provided to the algorithm and performance improvement, showing that in our case study prior knowledge affects two main properties, namely, the distance between the belief and the real state, and the mutual information between segment difficulty and action taken in the segment. This analysis aims to improve POMCP explainability, following the line of recently proposed eXplainable AI and, in particular, eXplainable planning. Finally, we analyze results on a synthetic case study and show how the proposed measures can improve the understanding about internal planning mechanisms

INVESTIGATING INNOVATIVE EVIDENCE SYNTHESIS METHODS: THE TRIAL SEQUENTIAL ANALYSIS, THE GRADE SYSTEM AND THE NETWORK META-ANALYSIS

Le revisioni sistematiche e meta-analisi sono i migliori disegni di studio per assistere il processo decisionale in ambito clinico. Pazienti, clinici, ricercatori e decisori politici dovrebbero privilegiare la revisione sistematica rispetto a altri tipi di disegno sperimentale in quanto permette di aggregare diversi studi primari contemporaneamente, incrementando la validit\ue0 interna ed esterna dei risultati. Inoltre, la meta-analisi aumenta la validit\ue0 statistica raggiungendo pi\uf9 alti livelli di potenza statistica e precisione rispetto ai singoli studi. Ci\uf2 significa comprendere meglio la grandezza dell\u2019effetto del trattamento e identificare il miglior intervento tra due, nel caso di meta-analisi standard, o tra molteplici, nel caso di network meta-analisi. Nonostante i numerosi vantaggi sopra riportati, la meta-analisi ha delle limitazioni importanti. La potenza e la precisione, infatti, dipendono da diversi elementi quali la dimensione campionaria degli studi, il numero di eventi, la variabilit\ue0 del campione e la relativa eterogeneit\ue0. Questi elementi sono condizioni imprescindibili e non modificabili dai revisori. Se uno o pi\uf9 di questi elementi sono problematici, la meta-analisi replicher\ue0 lo stesso problema, sebbene l\u2019entit\ue0 del problema stesso pu\uf2 diminuire grazie alla presenza di altri studi. Per esempio, le meta-analisi che includono studi con una numerosit\ue0 campionaria molto bassa saranno pi\uf9 propensi a diversi bias, quali lo small study effect e il publication bias. Inoltre molti studi clinici si propongo di ricercare modesti effetti di un intervento, che, generalmente, sono difficili da identificare: infatti, anche limitate variazioni nei dati di uno studio, o tra uno studio e un altro, possono risultare in bias che nascondono o alterano gli effetti di un intervento. Alla luce di questo background, la prima domanda di ricerca si \ue8 focalizzata sull\u2019adeguatezza del reporting degli studi randomizzati e controllati inclusi in revisioni sistematiche e meta-analisi, in particolare in termini di potenza statistica, rilevanza clinica e conclusivit\ue0 dei risultati. In secondo luogo, sono stati analizzati metodi innovativi per identificare e valutare meta-analisi sotto-potenziate, inconclusive e imprecise: tali metodi includono la Trial Sequential Analysis e il metodo GRADE (Grading of Recommendations Assessment, Development and Evaluation). Infine, \ue8 stata studiata e applicata una nuova tecnica meta-analitica per confrontare allo stesso tempo interventi multipli tra loro considerando sia l\u2019evidenza diretta sia l\u2019evidenza indiretta. Al fine di rispondere alle domande di ricerca proposte, si \ue8 passati dall\u2019unit\ue0 di analisi delle revisioni sistematiche, lo studio randomizzato e controllato, ai metodi di sintesi cumulativa delle evidenze. Il reporting inadeguato, le meta-analisi sotto-potenziate e le possibili discordanze tra evidenze dirette e indirette a partire dall\u2019analisi dei confronti testa-a-testa, possono alterare le decisioni cliniche portando a errori se viene meno un\u2019attenta disamina e ci si basa su un\u2019analisi statistica grossolana. La presente tesi \ue8 organizzata in tre sezioni principali: - Sezione 1: \ue8 stata valutato come il calcolo della dimensione campionaria sia stato riportato negli studi randomizzati e controllati che valutano l\u2019efficacia di interventi riabilitativi nella lombalgia e, tra gli studi adeguatamente riportati, come i risultati siano interpretati in termini di significativit\ue0 statistica e rilevanza clinica. - Sezione 2: sono state descritte, analizzate e applicate in diverse aree cliniche la Trial Sequential Analysis (TSA) e il metodo GRADE. Inoltre, \ue8 stata comparata la loro concordanza nel valutare e giudicare la qualit\ue0 dell\u2019evidenza. - Sezione 3: infine, considerato un campione di studi randomizzati e controllati che valutano l\u2019efficacia di interventi riabilitativi e farmacologici per la lombalgia, sono state combinate le evidenze dirette e indirette esistenti tramite la tecnica di network meta-analisi. Il focus di questa tesi \ue8 orientato ai metodi avanzati ed innovativi di sintesi delle evidenze. L\u2019introduzione e applicazione di questi metodi rappresentano la necessit\ue0 di rispondere al recente bisogno di risultati precisi e affidabili, a metodi trasparenti e di riferimento per valutare la qualit\ue0 e affidabilit\ue0 dell\u2019evidenza, e alla necessit\ue0 di confrontare numerosi interventi senza limitarsi a confronti binari.Systematic reviews and meta-analysis are the most appropriate and preferred study designs to inform clinical decision-making. Patients, clinicians, researchers and policymakers rely on this type of design since it aggregates several studies at the same time, increasing internal and external validity. Furthermore meta-analyses can increase statistical validity, reaching higher levels of power and precision as compared to single studies. This often means better understanding the magnitude of the treatment effect and its uncertainty therefore identifying the best intervention in pairwise or network (multiple) comparisons. Despite these advantages, meta-analyses also have limitations and shortcomings. Power and precision depend on several elements, such as size of studies, number of events, sample variability and underlying heterogeneity. These elements are precondition and cannot be modified by reviewers. If one or more of these elements are problematic, the meta-analysis will replicate the same problem, despite the severity of the problem might be diminished by the co-presence of multiple studies. For instance meta-analyses including several small studies will be prone to several biases, eg, small study effect and publication biases. Moreover actual studies often explore modest intervention effects, which are difficult to be identified: even limited perturbations of study data can result in biases that can hide or inflate intervention effects, sabotaging the decision-making process of health professionals. Against this background, we first wondered if RCTs included in systematic reviews and meta-analysis are adequately reported in terms of power and relevance/conclusiveness of findings. Secondly we explored how detect and assess underpowered, inconclusive and imprecise meta-analyses, using and comparing two modern approaches - Trial Sequential Analysis and the GRADE (Grading of Recommendations Assessment, Development and Evaluation). Third, we explored new meta-analytic techniques to contrast multiple interventions through direct and indirect evidence, in an extreme attempt to solve major limitations of a priori literature and lack of head to head trials. In order to answer these research questions, we moved from the unit of analysis of systematic reviews, the randomized controlled trial, to the methods to accumulate evidence. Inadequate reporting, underpowered meta-analyses and conflicting direct and indirect evidence beyond head-to-head comparisons can alter the clinical decision-making process unless proper assessment, analysis and critical interpretation are put in place. My dissertation is organized in three main Sections: - Section 1: We focused on how sample size calculations were reported in RCTs exploring the efficacy of low back pain rehabilitation interventions and, among those adequately reported, how findings were interpreted in terms of statistical significance and clinical relevance. - Section 2: We explored Trial Sequential Analysis and the GRADE approach in several medical areas. We compared the agreement of the approaches in evaluating the overall quality of evidence. - Section 3. We finally combined direct and indirect evidence on a sample of RCTs assessing rehabilitation interventions for low back pain through a network meta-analysis. This dissertation focuses on innovative advanced methods used in evidence synthesis science. These methods are partial answers to the need for precise and reliable results, standard and transparent methods to assess the body of evidence, and comparisons of multiple interventions in addition to pairwise comparisons