GloptiPoly 3: moments, optimization and semidefinite programming

We describe a major update of our Matlab freeware GloptiPoly for parsing generalized problems of moments and solving them numerically with semidefinite programming

A LEAST ABSOLUTE SHRINKAGE AND SELECTION OPERATOR (LASSO) FOR NONLINEAR SYSTEM IDENTIFICATION

Identification of parametric nonlinear models involves estimating unknown parameters and detecting its underlying structure. Structure computation is concerned with selecting a subset of parameters to give a parsimonious description of the system which may afford greater insight into the functionality of the system or a simpler controller design. In this study, a least absolute shrinkage and selection operator (LASSO) technique is investigated for computing efficient model descriptions of nonlinear systems. The LASSO minimises the residual sum of squares by the addition of a 1 penalty term on the parameter vector of the traditional 2 minimisation problem. Its use for structure detection is a natural extension of this constrained minimisation approach to pseudolinear regression problems which produces some model parameters that are exactly zero and, therefore, yields a parsimonious system description. The performance of this LASSO structure detection method was evaluated by using it to estimate the structure of a nonlinear polynomial model. Applicability of the method to more complex systems such as those encountered in aerospace applications was shown by identifying a parsimonious system description of the F/A-18 Active Aeroelastic Wing using flight test data

Bilevel programming for analysis of low-complexity control of linear systems with constraints

In this paper we use bilevel programming to find the maximum difference between a reference controller and a low-complexity controller in terms of the infinity-norm difference of their control laws. A nominal MPC for linear systems with constraints, and a robust MPC for linear systems with bounded additive noise are considered as reference controllers. For possible low-complexity controllers we discuss partial enumeration (PE), Voronoi/closest point, triangulation, linear controller with saturation, and others. A small difference in the norm between a low-complexity controller and a robust MPC may be used to guarantee closed-loop stability of the low-complexity controller and indicate that the behaviour or performance of the low-complexity controller will be similar to that of the reference one. We further discuss how bilevel programming may be used for closed-loop analysis of model reduction

From Particle Flow to Colour Flow in Top Events

A deeper understanding of the underlying event in $t\overline{t}$ pair production is expected to improve the current uncertainty on the measurements of the top quark mass. By selecting events with an electron, a muon and two b-tagged jets a high purity signal is obtained. The main properties of the underlying event are isolated and compared between data and different Pythia Monte Carlo Tunes. Discrepancies between the total number of charged particles for different models is observed. Furthermore a contribution of colour reconnection to the modeling of the average transverse momentum of the charged particles is identified

GloptiPoly 3: moments, optimization and semidefinite programming

International audienceWe describe a major update of our Matlab freeware GloptiPoly for parsing generalized problems of moments and solving them numerically with semidefinite programming

Prevalence of diarrhoeal pathogens among children under five years of age with and without diarrhoea in Guinea-Bissau

Background Childhood diarrhoea, a major cause of morbidity and mortality in low-income regions, remains scarcely studied in many countries, such as Guinea-Bissau. Stool sample drying enables later qPCR analyses of pathogens without concern about electricity shortages. Methods Dried stool samples of children under five years treated at the Bandim Health Centre in Bissau, Guinea-Bissau were screened by qPCR for nine enteric bacteria, five viruses, and four parasites. The findings of children having and not having diarrhoea were compared in age groups 0-11 and 12-59 months. Results Of the 429 children- 228 with and 201 without diarrhoea- 96.9% and 93.5% had bacterial, 62.7% and 44.3% viral, and 52.6% and 48.3% parasitic pathogen findings, respectively. Enteroaggregarive Escherichia coli (EAEC; 60.5% versus 66.7%), enteropathogenic E. coli (EPEC; 61.4% versus 62.7%), Campylobacter (53.2% versus 51.8%), and enterotoxigenic E. coli (ETEC; 54.4% versus 44.3%) were the most common bacterial pathogens. Diarrhoea was associated with enteroinvasive E. coli (EIEC)/Shigella (63.3%), astrovirus (75.0%), norovirus GII (72.6%) and Cryptosporidium (71.2%). The only pathogen associated with severe diarrhoea was EIEC/Shigella (p Conclusions Stool pathogens proved common among all the children regardless of them having diarrhoea or not. Author summary Diarrhoeal diseases rank second as cause of childhood mortality and morbidity in low-income countries, yet prospective cohort studies in children with and without diarrhea covering the large variety of diarrhoeal pathogens are limited. While some studies have been conducted among Guinea-Bissauan children, many of them were from the 1990s, when the coverage of the various pathogens was less extensive and the diagnostic methods less sensitive than the modern qPCR methods. We conducted an observational study with a large cohort and covered concomitantly the various bacterial, viral and parasitic agents, and analyzed their associations with the presence/absence of diarrhoeal symptoms and age groups. Importantly, the assay performed well with dried stool samples and, therefore, appears applicable for epidemiological studies in resource-poor regions. A pathogen finding was recorded for almost all (98%) children: bacteria in 97%, viruses in 59% and parasites in 51%. Ongoing diarrhoea was associated with findings of enteroninvasive Escherichia coli/Shigella, astrovirus, norovirus GII and Cryptosporidium. Differences were seen between age groups, infants and young children. The only pathogen associated with severe diarrhoea was enteroninvasive Escherichia coli/Shigella.Peer reviewe

Cystatin C is correlated with mortality in patients with and without acute kidney injury

BACKGROUND: Recent research has shown cystatin C to predict mortality and cardiovascular morbidity independent of renal function. The aim of this study was to evaluate the prognostic value of cystatin C on mortality in adult general ICU patients with acute kidney injury (AKI). We later expanded the study and included patients without signs of AKI. METHODS: A total of 845 ICU patients were analysed for cystatin C and classified according to the RIFLE criteria. Of these, 271 patients with either creatinine >150 micromol/l, urea >25 or anuria/oliguria entered the AKI cohort. The remaining 562 patients entered the non-AKI cohort. Both cohorts were divided into quartiles according to cystatin C at entry. In the non-AKI cohort, we split the highest cystatin C quartile into two. The relationship between the different cystatin C quartiles and mortality in patients with and without AKI was estimated by hazard ratios (HR) derived from the Cox proportional hazards regression model. RESULTS: A relationship between cystatin C and mortality was found in patients with and without AKI, being stronger in patients without AKI. In AKI patients, the HR comparing cystatin C above and below the median more than doubled from the second year on compared to the first year follow-up. After exclusion of patients in the non-AKI cohort with 'potential AKI' (creatinine >100 micromol/l or urea > 20 mmol/l), the correlation between cystatin C levels and risk of death was strengthened. CONCLUSIONS: Cystatin C is correlated with mortality independently of renal function measured by creatinine in patients entering the general ICU

Efficient Robustness Analysis of Electronic Networks in the Frequency Domain

International audienceRobustness analysis consists of analyzing if a system performs as it was intended to, even when parametric variations occur. Robustness is particularly interesting in critical applications, where decreased performance or failur cannot be tolerated, such as aerospace or nuclear industry electronic devices. In this context, it is important to develop methodologies to efficiently assess electronic systems robustness, even when the number of parameters or frequency ranges is large.In (Ferber et al, “Systematic LFT Derivation of Uncertain Electrical Circuits for Worst-Case Tolerance Analysis”, IEEE Transactions on EMC, vol. 57, issue 5, pp. 937-946, 2015), the authors presented a methodology to address the aforementioned problem that is efficient for a large number of parameters, since it is based on convex optimization. Upper and lower bounds on the system’s performance for a given frequency can be quickly obtained, even with hundreds of uncertain parameters. However, the computational time can still be large for problems that require a fine frequency grid i.e. a large frequency range with many considered frequencies.The contribution of this new work is to present an alternative methodology that overcomes the necessity of refining the frequency grid by computing bounds for the worst-case over a given frequency range. New forms of modeling the basic electrical components are proposed, such that an analysis on an interval of frequency can be carried out in one optimization run, instead of several runs on a fine frequency grid. Moreover, a new technique to overcome numerical issues is also presented.The method was implemented and tested on different problems related to conducted and radiated electromagnetic interference. The results are in accordance with the classical Monte Carlo method. The two main advantages of the proposed method related to Monte Carlo are: (1) the bounds are formally guaranteed to be respected in any combination of parameter values in a certain range and (2) the computational time required to compute the bounds is orders of magnitude lower than of Monte Carlo