Spline regression for zero-inflated models

We propose a regression model for count data when the classical generalized linear model approach is too rigid due to a high outcome of zero counts and a nonlinear influence of continuous covariates. Zero-Inflation is applied to take into account the presence of excess zeros with separate link functions for the zero and the nonzero component. Nonlinearity in covariates is captured by spline functions based on B-splines. Our algorithm relies on maximum-likelihood estimation and allows for adaptive box-constrained knots, thus improving the goodness of the spline fit and allowing for detection of sensitivity changepoints. A simulation study substantiates the numerical stability of the algorithm to infer such models. The AIC criterion is shown to serve well for model selection, in particular if nonlinearities are weak such that BIC tends to overly simplistic models. We fit the introduced models to real data of children's dental sanity, linking caries counts with the so-called Body-Mass-Index (BMI) and other socioeconomic factors. This reveals a puzzling nonmonotonic influence of BMI on caries counts which is yet to be explained by clinical experts

Factors influencing take-up of free school meals in primary- and secondary-school children in England.

OBJECTIVE: The present study sought to explore the factors that influence registration for free school meals and the subsequent take-up following registration in England. DESIGN: The research design consisted of two phases, a qualitative research phase followed by an intervention phase. Findings are presented from the qualitative research phase, which comprised interviews with head teachers, school administrators, parents and focus groups with pupils. SETTING: The study took place in four primary schools and four secondary schools in Leeds, UK. SUBJECTS: Participants included head teachers, school administrators, parents and pupils. RESULTS: Findings suggested that parents felt the registration process to be relatively straightforward although many secondary schools were not proactive in promoting free school meals. Quality and choice of food were regarded by both pupils and parents as significant in determining school meal choices, with stigma being less of an issue than originally anticipated. CONCLUSIONS: Schools should develop proactive approaches to promoting free school meals and attention should be given not only to the quality and availability of food, but also to the social, cultural and environmental aspects of dining. Processes to maintain pupils' anonymity should be considered to allay parents' fear of stigma

Interventions to increase free school meal take-up

Purpose: The purpose of this paper is to design and implement interventions to increase free school meal (FSM) uptake in pilot schools. This paper describes the interventions, reports on acceptability (as perceived by school working parties) and explores the process of implementing change. Design/methodology/approach: The research consisted of two phases, an exploratory phase followed by an intervention phase. Findings from the latter are presented. Ten pilot schools (five primary and five secondary) in Leeds, England were recruited. Each established a working party, examined current claiming processes and implemented individualised action plans. This paper draws on the final action plans and interviews/focus groups with working parties. Findings: Interventions to improve FSM claiming process, minimise discrimination and maximise awareness were designed. The majority were implemented successfully, the exception being amending anti-bullying policies. Creative ways of delivering interventions were demonstrated. The process of change was effective, critical factors being having individualised action plans that allowed flexibility in implementation, reflecting on current claiming processes, and setting up working parties. Practical implications: Ways of working with schools to increase FSM uptake and more generally improve nutritional policies are suggested. Amending claiming systems in schools is recommended as is greater pupil and parent involvement in nutrition policies. Originality/value: An estimated 300,000 UK children do not take FSMs they are entitled to – with many schools unaware of the issue. This study worked with schools to discover how to address this issue and evaluated the perceived acceptability and feasibility of the approach

A possible observational bias in the estimation of the virial parameter in virialized clumps

The dynamics of massive clumps, the environment where massive stars originate, is still unclear. Many theories predict that these regions are in a state of near-virial equilibrium, or near energy equi-partition, while others predict that clumps are in a sub-virial state. Observationally, the majority of the massive clumps are in a sub-virial state with a clear anti-correlation between the virial parameter $\alpha_{vir}$ and the mass of the clumps $M_{c}$, which suggests that the more massive objects are also the more gravitationally bound. Although this trend is observed at all scales, from massive clouds down to star-forming cores, theories do not predict it. In this work we show how, starting from virialized clumps, an observational bias is introduced in the specific case where the kinetic and the gravitational energies are estimated in different volumes within clumps and how it can contribute to the spurious $\alpha_{vir}-M_{c}$ anti-correlation in these data. As a result, the observed effective virial parameter $\tilde{\alpha}_{eff}<\alpha_{vir}$, and in some circumstances it might not be representative of the virial state of the observed clumps.Comment: A&A letter, accepte

FEATURE SELECTION APPLIED TO THE TIME-FREQUENCY REPRESENTATION OF MUSCLE NEAR-INFRARED SPECTROSCOPY (NIRS) SIGNALS: CHARACTERIZATION OF DIABETIC OXYGENATION PATTERNS

Diabetic patients might present peripheral microcirculation impairment and might benefit from physical training. Thirty-nine diabetic patients underwent the monitoring of the tibialis anterior muscle oxygenation during a series of voluntary ankle flexo-extensions by near-infrared spectroscopy (NIRS). NIRS signals were acquired before and after training protocols. Sixteen control subjects were tested with the same protocol. Time-frequency distributions of the Cohen's class were used to process the NIRS signals relative to the concentration changes of oxygenated and reduced hemoglobin. A total of 24 variables were measured for each subject and the most discriminative were selected by using four feature selection algorithms: QuickReduct, Genetic Rough-Set Attribute Reduction, Ant Rough-Set Attribute Reduction, and traditional ANOVA. Artificial neural networks were used to validate the discriminative power of the selected features. Results showed that different algorithms extracted different sets of variables, but all the combinations were discriminative. The best classification accuracy was about 70%. The oxygenation variables were selected when comparing controls to diabetic patients or diabetic patients before and after training. This preliminary study showed the importance of feature selection techniques in NIRS assessment of diabetic peripheral vascular impairmen

Many-body approach to infinite non-periodic systems: application to the surface of semi-infinite jellium

A method to implement the many-body Green function formalism in the GW approximation for infinite non periodic systems is presented. It is suitable to treat systems of known ``asymptotic'' properties which enter as boundary conditions, while the effects of the lower symmetry are restricted to regions of finite volume. For example, it can be applied to surfaces or localized impurities. We illustrate the method with a study of the surface of semi-infinite jellium. We report the dielectric function, the effective potential and the electronic self-energy discussing the effects produced by the screening and by the charge density profile near the surface.Comment: 11 pages, 4 figure