1,721,324 research outputs found
MEDICAL IMAGING EQUIPMENT IN ITALY: STATE OF ART OF INSTALLED BASE AND RENEWAL STRATEGIES
No full textFidelity and Reversibility in the Three Body Problem
No full textWe use the Reversibility Error Method and the Fidelity to analyze the global effects of a small
perturbation in a non-integrable system. Both methods have already been proposed and used
in the literature but the aim of this paper is to compare them in a physically significant example
adding some considerations on the equivalence, observed in this case, between round-off and random
perturbations.
As a paradigmatic example we adopt the restricted planar circular three body problem. The
cumulative effect of random perturbations or round-off leads to a divergence of the perturbed
orbit from the reference one. Rather than computing the distance of the perturbed orbit from
the reference one, after a given number n of iterations, a procedure we name the Forward Error
Method (FEM), we measure the distance of the reversed orbit (n periods forward and backward)
from the initial point. This approach, that we name Reversibility Error Method (REM), does
not require the computation of the unperturbed map. The loss of memory of the perturbed map
is quantified by the Fidelity decay rate whose computation requires a statistical average over an
invariant region. Two distinct definitions of Fidelity are given. The asymptotic equivalence of
REM and FEM is analytically proved for linear symplectic maps with random perturbations. For
a given map, the REM plot provides a picture of the dynamic stability regions in the phase space,
very easy to obtain for any kind of perturbation and very simple to implement numerically. The
REM and FEM for linear symplectic maps are proved to be asymptotically equivalent. The global
error growth follows a power law in the regions of integrable (or quasi integrable) motion and an
exponential law in the regions of chaotic motion. We prove that the power law exponent is 3/2 for a
generic anisochronous system, but drops down to 1/2 if the system is isochronous. Correspondingly
the Fidelity F(t) exhibits an exponential decay and −ln F(t) grows just as the square of the FEM
or REM error. The Reversibility Error and Fidelity can be used for a quantitative analysis of
dynamical systems and are suited to investigate the transition regions from chaotic to regular
motion even for Hamiltonian systems with many degrees of freedom such as the N-body problem
Scoping review and bibliometric analysis of Big Data applications for Medication adherence: An explorative methodological study to enhance consistency in literature
Full text linkBackground: Medication adherence has been studied in different settings, with different approaches, and applying different methodologies. Nevertheless, our knowledge and efficacy are quite limited in terms of measuring and evaluating all the variables and components that affect the management of medication adherence regimes as a complex phenomenon. The study aim is mapping the state-of-the-art of medication adherence measurement and assessment methods applied in chronic conditions. Specifically, we are interested in what methods and assessment procedures are currently used to tackle medication adherence. We explore whether Big Data techniques are adopted to improve decision-making procedures regarding patients' adherence, and the possible role of digital technologies in supporting interventions for improving patient adherence and avoiding waste or harm. Methods: A scoping literature review and bibliometric analysis were used. Arksey and O'Malley's framework was adopted to scope the review process, and a bibliometric analysis was applied to observe the evolution of the scientific literature and identify specific characteristics of the related knowledge domain. Results: A total of 533 articles were retrieved from the Scopus academic database and selected for the bibliometric analysis. Sixty-one studies were identified and included in the final analysis. The Morisky medication adherence scale (36%) was the most frequently adopted baseline measurement tool, and cardiovascular/hypertension disease, the most investigated illness (38%). Heterogeneous findings emerged from the types of study design and the statistical methodologies used to assess and compare the results. Conclusions: Our findings reveal a lack of Big Data applications currently deployed to address or measure medication adherence in chronic conditions. Our study proposes a general framework to select the methods, measurements and the corpus of variables in which the treatment regime can be analyzed
Asymptotic distribution of global errors in the numerical computations of dynamical systems
Full text linkWe propose an analysis of the effects introduced by finite-accuracy and round-off arithmetic on numerical computations of discrete dynamical systems. Our method, which uses
the statistical tool of the decay of fidelity, computes the error by directly comparing the
numerical orbit with the exact one (or, more precisely, with another numerical orbit computed with a much higher accuracy). Furthermore, as a model of the effects of round-off
arithmetic on the map, we also consider a random perturbation of the exact orbit with
an additive noise, for which exact results can be obtained for some prototype maps. We
investigate the decay laws of fidelity and their relationship with the error probability distribution for regular and chaotic maps, for both additive and numerical noise. In particular,
for regular maps we find an exponential decay for additive noise, and a power-law decay
for numerical noise. For chaotic maps, numerical noise is equivalent to additive noise, and
our method is suitable for identifying a threshold for the reliability of numerical results, i.e.,
the number of iterations below which global errors can be ignored. This threshold grows
linearly with the number of bits used to represent real numbers
Nekhoroshev estimate for isochronous non resonant symplectic maps
No full textWe prove that non resonant isochronous symplectic maps in a neighborhood of an elliptic fixed point are stable for exponentially long times with the inverse of the distance from the fixed point. In the proof we make use of the majorant series method together with an idea for optimizing remainder estimates first applied to Hamiltonian problems by Nekhoroshev
Cost-Effectiveness of Direct Non-Vitamin K Oral Anticoagulants Versus Vitamin K Antagonists for the Management of Patients with Non-Valvular Atrial Fibrillation Based on Available “Real-World” Evidence: The Italian National Health System Perspective
No full textBackground and objective: The increasing availability of real-world evidence (RWE) about safety and effectiveness of direct non-vitamin K oral anticoagulants (DOACs) for the management of atrial fibrillation (AF) offers the opportunity to better understand the clinical and economic implications of DOACs versus vitamin K antagonists (VKAs). The objective of this study was to compare the economic implications of DOACs and VKAs using data from real-world evidence in patients with AF. Methods: A Markov model simulating the lifetime course of patients diagnosed with non-valvular AF was used to evaluate the cost-effectiveness of DOACs (i.e., rivaroxaban, dabigatran and apixaban) versus VKAs from the Italian National Health System (INHS) perspective. The model was made up of data from the literature and a meta-analysis of RWE on the incidence of stroke/systemic embolism (SE), major bleeding (MB), intracranial haemorrhage (ICH) and all-cause mortality (ACM); direct costs included drug costs, costs for drug monitoring, and management of events from official national lists. One-way and probabilistic sensitivity analyses (PSA) were used to assess the robustness of the results. Results: Results from the meta-analysis showed that apixaban had a high probability of being the most effective for stroke/SE, MB and ACM. Despite their higher acquisition costs, the cost-effectiveness analysis showed all DOACs involved a saving when compared with VKAs, with per-patient savings ranging between €4647 (rivaroxaban) to €6086 (apixaban). Moreover, all DOACs indicated a gain both in quality-adjusted life-years and life-years. According to PSA, findings related to apixaban were consistent, while for dabigatran and rivaroxaban PSA revealed a higher degree of uncertainty. Conclusions: The beneficial effect of DOACs on containing events showed in RWE had the potential to offset drug-related costs, thus improving the sustainability of treatment for non-valvular AF in daily clinical practice
From Innovation to Integration: A Case Study of Digital Health Technologies in the Trentino Healthcare System
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