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Search Results: 1 - 10 of 212 matches for " Nathanael Lapidus "
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Prognostic Accuracy of WHO Growth Standards to Predict Mortality in a Large-Scale Nutritional Program in Niger
Nathanael Lapidus,Francisco J Luquero,Valérie Gaboulaud,Susan Shepherd,Rebecca F Grais
PLOS Medicine , 2009, DOI: 10.1371/journal.pmed.1000039
Abstract: Background Important differences exist in the diagnosis of malnutrition when comparing the 2006 World Health Organization (WHO) Child Growth Standards and the 1977 National Center for Health Statistics (NCHS) reference. However, their relationship with mortality has not been studied. Here, we assessed the accuracy of the WHO standards and the NCHS reference in predicting death in a population of malnourished children in a large nutritional program in Niger. Methods and Findings We analyzed data from 64,484 children aged 6–59 mo admitted with malnutrition (<80% weight-for-height percentage of the median [WH]% [NCHS] and/or mid-upper arm circumference [MUAC] <110 mm and/or presence of edema) in 2006 into the Médecins Sans Frontières (MSF) nutritional program in Maradi, Niger. Sensitivity and specificity of weight-for-height in terms of Z score (WHZ) and WH% for both WHO standards and NCHS reference were calculated using mortality as the gold standard. Sensitivity and specificity of MUAC were also calculated. The receiver operating characteristic (ROC) curve was traced for these cutoffs and its area under curve (AUC) estimated. In predicting mortality, WHZ (NCHS) and WH% (NCHS) showed AUC values of 0.63 (95% confidence interval [CI] 0.60–0.66) and 0.71 (CI 0.68–0.74), respectively. WHZ (WHO) and WH% (WHO) appeared to provide higher accuracy with AUC values of 0.76 (CI 0.75–0.80) and 0.77 (CI 0.75–0.80), respectively. The relationship between MUAC and mortality risk appeared to be relatively weak, with AUC = 0.63 (CI 0.60–0.67). Analyses stratified by sex and age yielded similar results. Conclusions These results suggest that in this population of children being treated for malnutrition, WH indicators calculated using WHO standards were more accurate for predicting mortality risk than those calculated using the NCHS reference. The findings are valid for a population of already malnourished children and are not necessarily generalizable to a population of children being screened for malnutrition. Future work is needed to assess which criteria are best for admission purposes to identify children most likely to benefit from therapeutic or supplementary feeding programs.
Planning for the next influenza H1N1 season: a modelling study
Fabrice Carrat, Camille Pelat, Daniel Levy-Bruhl, Isabelle Bonmarin, Nathanael Lapidus
BMC Infectious Diseases , 2010, DOI: 10.1186/1471-2334-10-301
Abstract: This was a modelling study based on data on medical visits for influenza-like illness collected by the French General Practitioner Sentinel network, as well as pandemic H1N1 vaccination coverage rates, and an individual-centred model devoted to influenza. We estimated infection attack rates during the first 2009 pandemic H1N1 season in France, and the rates of pre- and post-exposure immunity. We then simulated various scenarios in which a pandemic influenza H1N1 virus would be reintroduced into a population with varying levels of protective cross-immunity, and considered the impact of extending influenza vaccination.During the first pandemic season in France, the proportion of infected persons was 18.1% overall, 38.3% among children, 14.8% among younger adults and 1.6% among the elderly. The rates of pre-exposure immunity required to fit data collected during the first pandemic season were 36% in younger adults and 85% in the elderly. We estimated that the rate of post-exposure immunity was 57.3% (95% Confidence Interval (95%CI) 49.6%-65.0%) overall, 44.6% (95%CI 35.5%-53.6%) in children, 53.8% (95%CI 44.5%-63.1%) in younger adults, and 87.4% (95%CI 82.0%-92.8%) in the elderly.The shape of a second season would depend on the degree of persistent protective cross-immunity to descendants of the 2009 H1N1 viruses. A cross-protection rate of 70% would imply that only a small proportion of the population would be affected. With a cross-protection rate of 50%, the second season would have a disease burden similar to the first, while vaccination of 50% of the entire population, in addition to the population vaccinated during the first pandemic season, would halve this burden. With a cross-protection rate of 30%, the second season could be more substantial, and vaccination would not provide a significant benefit.These model-based findings should help to prepare for a second pandemic season, and highlight the need for studies of the different components of immune protection.
A Room to Grow: The Residential Density-dependence of Childbearing in Europe and the United States
Nathanael Lauster
Canadian Studies in Population , 2010,
Abstract: I argue that cultural processes linked to the demographic transition produce new density-dependent fertility dynamics. In particular, childbearing becomes dependent upon residential roominess. This relationship is culturally specific, and I argue that the cultural nature of this relationship means that professional and managerial classes are likely to be particularly influenced by residential roominess, while immigrants are less likely to be influenced. I test hypotheses linking residential roominess to the presence of an “own infant” in the household using census data from the Austria, Greece, Portugal, Spain, and the United States. Roominess predicts fertility in all countries, but to differing degrees.
An invariance principle for Azéma martingales
Nathanael Enriquez
Mathematics , 2005,
Abstract: An invariance principle for Az\'{e}ma martingales is presented as well as a new device to construct solutions of Emery's structure equations.
Emergence of giant cycles and slowdown transition in random transpositions and $k$-cycles
Nathanael Berestycki
Mathematics , 2010,
Abstract: Consider the random walk on the permutation group obtained when the step distribution is uniform on a given conjugacy class. It is shown that there is a critical time at which two phase transitions occur simultaneously. On the one hand, the random walk slows down abruptly (i.e., the acceleration drops from 0 to -\infty at this time as n tends to \infty). On the other hand, the largest cycle size changes from microscopic to giant. The proof of this last result is both considerably simpler and more general than in a previous result of Oded Schramm (2005) for random transpositions. It turns out that in the case of random k-cycles, this critical time is proportional to 1/[k(k-1)], whereas the mixing time is known to be proportional to 1/k.
Diffusion in planar Liouville quantum gravity
Nathanael Berestycki
Mathematics , 2013,
Abstract: We construct the natural diffusion in the random geometry of planar Liouville quantum gravity. Formally, this is the Brownian motion in a domain $D$ of the complex plane for which the Riemannian metric tensor at a point $z \in D$ is given by $\exp (\gamma h(z) - \frac12 \gamma^2 \E (h(z)^2))$. Here $h$ is an instance of the Gaussian Free Field on $D$ and $\gamma \in (0,2)$ is a parameter. We show that the process is almost surely continuous and enjoys certain conformal invariance properties. We also estimate the Hausdorff dimension of times that the diffusion spends in the thick points of the Gaussian Free Field, and show that it spends Lebesgue-almost all its time in the set of $\gamma$-thick points, almost surely. The diffusion is constructed by a limiting procedure after regularisation of the Gaussian Free Field. The proof is inspired by arguments of Duplantier--Sheffield for the convergence of the Liouville quantum gravity measure, previous work on multifractal random measures, and relies also on estimates on the occupation measure of planar Brownian motion by Dembo, Peres, Rosen and Zeitouni. A similar but deeper result has been independently and simultaneously proved by Garban, Rhodes and Vargas.
Representations of $\Aut(\M)$-Invariant Measures: Part 1
Nathanael Ackerman
Mathematics , 2015,
Abstract: In this paper we generalize the Aldous-Hoover-Kallenberg theorem concerning representations of distributions of exchangeable arrays via collections of measurable maps. We give criteria when such a representation theorem exists for arrays which need only be preserved by a closed subgroup of $\Sym{\Nats}$. Specifically, for a countable structure $\M$ we introduce the notion of an \emph{$\Aut(\M)$-recipe}, which is an $\Aut(\M)$-invariant array obtained via a collection of measurable functions indexed by the $\Aut(\M)$-orbits in $\M$. We further introduce the notion of a \emph{free structure} and then show that if $\M$ is free then every $\Aut(\M)$-invariant measure on an $\Aut(\M)$-space is the distribution of an $\Aut(\M)$-recipe. We also show that if a measure is the distribution of an $\Aut(\M)$-recipe it must be the restriction of a measure on a free structure.
A simple construction of the Fractional Brownian motion
Enriquez Nathanael
Mathematics , 2002,
Abstract: In this work we introduce correlated random walks on $\Z$. When picking suitably at random the coefficient of correlation, and taking the average over a large number of walks, we obtain a discrete Gaussian process, whose scaling limit is the fractional Brownian motion. We have to use two radically different models for both cases ${1\over2}\leq H<1$ and $0
Recent progress in coalescent theory
Nathanael Berestycki
Mathematics , 2009,
Abstract: Coalescent theory is the study of random processes where particles may join each other to form clusters as time evolves. These notes provide an introduction to some aspects of the mathematics of coalescent processes and their applications to theoretical population genetics and other fields such as spin glass models. The emphasis is on recent work concerning in particular the connection of these processes to continuum random trees and spatial models such as coalescing random walks.
Yo tengo sentido, tengo rima : Cano Estremera and the Art of the Soneo
Benjamin Lapidus
Centro Journal , 2004,
Abstract: Calling himself El due o del soneo, the boss of vocal improvisation, the Puerto Rican singer, Carlos Cano Estremera, is at the forefront of many innovations in soneos. For the uninitiated, a soneo is a vocal improvisation sung by a lead singer during the montuno, or call-and-response section in Afro-Cuban son-based musics, commercially referred to as salsa. As he is always up for a good duel, planned or unforseen, the results of Cano s duelos have been recorded both legally and illegally and spread throughout the world by salsa fans. Through conversations with Cano and a look at several techniques he uses when improvising, this article shows Cano Esteremera s improvisational framework to be a synthesis of previous soneros as well as singers and musicians from beyond the realm of salsa. His style can be summed up as unique and creative while remaining in the tradition.
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