185 research outputs found
A nonparametric approach for model individualization in an artificial pancreas
The identification of patient-tailored linear time invariant glucose-insulin models is investigated for type 1 diabetic patients, that are characterized by a substantial inter-subject variability. The individualized linear models are identified by considering a novel kernel-based nonparametric approach and are compared with a linear time invariant average model in terms of prediction performance by means of the coefficient of determination, fit, positive and negative max errors, and root mean squared error. Model identification and validation are based on in-silico data collected from the adult virtual population of the UVA/Padova simulator. The data generation involves a protocol designed to produce a sufficient input excitation without compromising patient safety, compatible also with real life scenarios. The identified models are exploited to synthesize an individualized Model Predictive Controller (MPC) for each patient, which is used in an Artificial Pancreas to maintain the blood glucose concentration within an euglycemic range. The MPC used in several clinical studies, synthesized on the basis of a non-individualized average linear time invariant model, is also considered as reference. The closed-loop control performance is evaluated in an in-silico study on the adult virtual population of the UVA/Padova simulator in a perturbed scenario, in which the MPC is blind to random variations of insulin sensitivity in each virtual patient. © 2015, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved
Dynamics of systems with isotropic competing interactions in an external field: a Langevin approach
We study the Langevin dynamics of a ferromagnetic Ginzburg-Landau Hamiltonian
with a competing long-range repulsive term in the presence of an external
magnetic field. The model is analytically solved within the self consistent
Hartree approximation for two different initial conditions: disordered or zero
field cooled (ZFC), and fully magnetized or field cooled (FC). To test the
predictions of the approximation we develop a suitable numerical scheme to
ensure the isotropic nature of the interactions. Both the analytical approach
and the numerical simulations of two-dimensional finite systems confirm a
simple aging scenario at zero temperature and zero field. At zero temperature a
critical field is found below which the initial conditions are relevant
for the long time dynamics of the system. For a logarithmic growth of
modulated domains is found in the numerical simulations but this behavior is
not captured by the analytical approach which predicts a growth law at
Antideuterons as a Signature of Supersymmetric Dark Matter
Once the energy spectrum of the secondary component is well understood,
measurements of the antiproton cosmic-ray flux at the Earth will be a powerful
way to indirectly probe for the existence of supersymmetric relics in the
galactic halo. Unfortunately, it is still spoilt by considerable theoretical
uncertainties. As shown in this work, searches for low-energy antideuterons
appear in the mean time as a plausible alternative, worth being explored. Above
a few GeV/n, a dozen spallation antideuterons should be collected by the future
AMS experiment on board ISSA. For energies less than about 3 GeV/n, the
antideuteron spallation component becomes negligible and may be supplanted by a
potential supersymmetric signal. If a few low-energy antideuterons are
discovered, this should be seriously taken as a clue for the existence of
massive neutralinos in the Milky Way.Comment: 16 pages, 9 figure
Observability and nonlinear filtering
This paper develops a connection between the asymptotic stability of
nonlinear filters and a notion of observability. We consider a general class of
hidden Markov models in continuous time with compact signal state space, and
call such a model observable if no two initial measures of the signal process
give rise to the same law of the observation process. We demonstrate that
observability implies stability of the filter, i.e., the filtered estimates
become insensitive to the initial measure at large times. For the special case
where the signal is a finite-state Markov process and the observations are of
the white noise type, a complete (necessary and sufficient) characterization of
filter stability is obtained in terms of a slightly weaker detectability
condition. In addition to observability, the role of controllability in filter
stability is explored. Finally, the results are partially extended to
non-compact signal state spaces
Sneutrino cold dark matter, a new analysis: relic abundance and detection rates
We perform a new and updated analysis of sneutrinos as dark matter
candidates, in different classes of supersymmetric models. We extend previous
analyses by studying sneutrino phenomenology for full variations of the
supersymmetric parameters which define the various models. We first revisit the
standard Minimal Supersymmetric Standard Model, concluding that sneutrinos are
marginally compatible with existing experimental bounds, including direct
detection, provided they compose a subdominant component of dark matter. We
then study supersymmetric models with the inclusion of right-handed fields and
lepton-number violating terms. Simple versions of the lepton-number-violating
models do not lead to phenomenology different from the standard case when the
neutrino mass bounds are properly included. On the contrary, models with
right-handed fields are perfectly viable: they predict sneutrinos which are
compatible with the current direct detection sensitivities, both as subdominant
and dominant dark matter components. We also study the indirect detection
signals for such successful models: predictions for antiproton, antideuteron
and gamma-ray fluxes are provided and compared with existing and future
experimental sensitivities. The neutrino flux from the center of the Earth is
also analyzed.Comment: 72 pages, 50 figures. The version on the archive has low-resolution
figures. The paper with high resolution figures may be found through
http://www.to.infn.it/~arina/papers or
http://www.to.infn.it/~fornengo/Research/paperlist.htm
The risk stratification of adverse neonatal outcomes in women with gestational diabetes (STRONG) study
Aims: To assess the risk of adverse neonatal outcomes in women with gestational diabetes (GDM) by identifying subgroups of women at higher risk to recognize the characteristics most associated with an excess of risk. Methods: Observational, retrospective, multicenter study involving consecutive women with GDM. To identify distinct and homogeneous subgroups of women at a higher risk, the RECursive Partitioning and AMalgamation (RECPAM) method was used. Overall, 2736 pregnancies complicated by GDM were analyzed. The main outcome measure was the occurrence of adverse neonatal outcomes in pregnancies complicated by GDM. Results: Among study participants (median age 36.8 years, pre-gestational BMI 24.8 kg/m2), six miscarriages, one neonatal death, but no maternal death was recorded. The occurrence of the cumulative adverse outcome (OR 2.48, 95% CI 1.59–3.87), large for gestational age (OR 3.99, 95% CI 2.40–6.63), fetal malformation (OR 2.66, 95% CI 1.00–7.18), and respiratory distress (OR 4.33, 95% CI 1.33–14.12) was associated with previous macrosomia. Large for gestational age was also associated with obesity (OR 1.46, 95% CI 1.00–2.15). Small for gestational age was associated with first trimester glucose levels (OR 1.96, 95% CI 1.04–3.69). Neonatal hypoglycemia was associated with overweight (OR 1.52, 95% CI 1.02–2.27) and obesity (OR 1.62, 95% CI 1.04–2.51). The RECPAM analysis identified high-risk subgroups mainly characterized by high pre-pregnancy BMI (OR 1.68, 95% CI 1.21–2.33 for obese; OR 1.38 95% CI 1.03–1.87 for overweight). Conclusions: A deep investigation on the factors associated with adverse neonatal outcomes requires a risk stratification. In particular, great attention must be paid to the prevention and treatment of obesity
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