Estimation in a class of nonlinear heteroscedastic time series models

Parameter estimation in a class of heteroscedastic time series models is investigated. The existence of conditional least-squares and conditional likelihood estimators is proved. Their consistency and their asymptotic normality are established. Kernel estimators of the noise's density and its derivatives are defined and shown to be uniformly consistent. A simulation experiment conducted shows that the estimators perform well for large sample size.Comment: Published in at http://dx.doi.org/10.1214/07-EJS157 the Electronic Journal of Statistics (http://www.i-journals.org/ejs/) by the Institute of Mathematical Statistics (http://www.imstat.org

Autre cause de mort subite du nourrisson: à propos d’un cas clinique de syndrome du QT long congenital

Le syndrome du QT long congénital est une maladie rythmique liée à une mutation génétique et caractérisée par un espace QT allongé sur l'électrocardiogramme, des arythmies malignes type torsade de pointe et  fibrillation ventriculaire entraînant une mort subite. Les gènes impliqués dans ces mutations codent pour des sous unités des canaux ioniques responsables de l'activité électrique cardiaque. Le diagnostic est basé sur l'électrocardiogramme, une enquête familiale et l'étude génétique. Le traitement repose sur les  bêtabloquants, la sympathectomie et le stimulateur cardiaque. Nous rapportons le cas d'un nourrisson de 2 ans retrouvé en état de mort apparente. Nous discutons de sa prise en charge initiale, de l'enquête familiale et de son suivi ultérieur.Key words: Syndrome du QT long, canalopathie rythmique, mort subit

A Nonparametric Goodness-of-fit Test for a Class of Parametric Autoregressive Models

We derive a nonparametric test for discriminating between generalized autoregressive models. This test is based on a suitably normalized sum of residuals. The null distribution and the power of the test under both fixed and a sequence of local alternatives are studied under mild stationarity and $\alpha$--mixing conditions. This procedure can be applied to testing linear models against nonlinear models or certain nonlinear models against others. Numerical simulations show that the proposed test is powerful against most of the alternatives considered

Anévrysme de l’aorte thoracique d’origine traumatique: cas clinique suspect

Dans ce travail nous rapportons le cas d'un homme d'origine africaine du nord, âgé de 51 ans, qui s'est présenté à l'urgence pour des douleurs thoraciques constantes depuis un jour. Dans son anamnèse on note un enrouement de la voix depuis deux mois, une notion d'accident de circulation il y a environ dix ans. Patient sportif, fait de la boxe et travaille comme agent de sécurité dans une boite de nuit. La radiographie du thorax et l'angio-scanner thoracique montrent un volumineux anévrisme non compliqué de la crosse et du tiers distal de l'aorte thoracique descendante (7cmx7.8cm en vue axiale). Le patient a bénéficié d'une cure chirurgicale de ce volumineux anévrisme de l'aorte thoracique. Nous discutons des étiologies, des mesures cliniques et para cliniques qui permet le diagnostic de cette entité clinique rare pouvant être une erreur diagnostique pour un médecin urgentiste

Spermatogenesis and sertoli cell activity in mice lacking Sertoli cell receptors for follicle stimulating hormone and androgen

Spermatogenesis in the adult male depends on the action of FSH and androgen. Ablation of either hormone has deleterious effects on Sertoli cell function and the progression of germ cells through spermatogenesis. In this study we generated mice lacking both FSH receptors (FSHRKO) and androgen receptors on the Sertoli cell (SCARKO) to examine how FSH and androgen combine to regulate Sertoli cell function and spermatogenesis. Sertoli cell number in FSHRKO-SCARKO mice was reduced by about 50% but was not significantly different from FSHRKO mice. In contrast, total germ cell number in FSHRKO-SCARKO mice was reduced to 2% of control mice (and 20% of SCARKO mice) due to a failure to progress beyond early meiosis. Measurement of Sertoli cell-specific transcript levels showed that about a third were independent of hormonal action on the Sertoli cell, whereas others were predominantly androgen dependent or showed redundant control by FSH and androgen. Results show that FSH and androgen act through redundant, additive, and synergistic regulation of spermatogenesis and Sertoli cell activity. In addition, the Sertoli cell retains a significant capacity for activity, which is independent of direct hormonal regulation

Fistule artério-veineuse post-traumatique associée à un pseudo-anévrysme de l’artère brachiale : A propos d’un cas à l’Hôpital Général de Douala: Post-traumatic pseudo-aneurysm of brachial artery with arteriovenous fistula: a case report in Cameroon setting

Vascular wounds are a reality of open or closed trauma affecting the vascular axes. These vascular lesions may go unnoticed and discovered at complicated stages. Pseudoaneurysm and arteriovenous fistula represent two potential but rarely associated complications. We report the case of a 26-year-old patient with a pseudoaneurysm associated with an arteriovenous fistula following a gunshot wound. We recall the diagnostic issues and pitfalls to avoid in the management. Les plaies vasculaires sont une réalité des traumatismes ouverts ou fermés touchant les axes vasculaires. Ces lésions vasculaires peuvent passer inaperçus et découvertes au stade complications. Le faux anévrysme et la fistule artério-veineuse représentent deux complications potentielles mais rarement associées. Nous rapportons le cas d’un patient de 26 ans présentant un faux anévrysme associé à une fistule artério-veineuse suite à une plaie par arme à feu. Nous rappelons les enjeux diagnostics et les pièges à éviter dans la prise en charge

Bayesian Modelling of PWR Vessels Flaw Distributions

We present a full Bayesian method for estimating the density and size distribution of subclad-flaws in French Pressurized Water Reactor (PWR) vessels. This model takes into account in service inspection (ISI) data, a flaw size-dependent probability of detection function (different function types are possible) with a threshold of detection, and a flaw sizing error distribution (different distribution types are possible). It is identified through a Markov Chain Monte Carlo (MCMC) algorithm. The article includes discussion for choosing the prior distribution parameters and an illustrative application is presented highlighting its ability to provide good parameter estimates even when a small number of flaws is observed

Delayed maintenance modelling considering speed restriction for a railway section

The deterioration of track geometry depends on several factors of which the speed of the train is one. Imposing a speed restriction can slow down the track deterioration and allows a longer survival time before a serious condition is achieved. Preventive maintenance delays can be authorized during the survival time. However, speed restrictions also reduce the system throughput. On the other hand, a longer interval between preventive maintenance activities has a lower maintenance action cost and it also enables grouping the maintenance activities to save set-up costs as well as system down time. If the repair delay is too long, it may cause unacceptable conditions on the track and lead to higher maintenance costs and accidents. Therefore, it is interesting to assess the effect of a speed restriction on the delayed maintenance strategies for a railway track section. We want to solve a maintenance optimization problem to find the optimal tuning of the maintenance delay time and imposition of a speed restriction. To this aim, a delayed maintenance model is developed, in which track deterioration depends on the train speed and the number of passing trains. The model is used to determine an optimal speed restriction strategy and a preventive repair delay for the optimization of the system benefit and unavailability. Coloured Petri Nets (CPN) are adopted to model the maintenance and operation of the railway track section. The CPN model describes the gradual track deterioration as a stochastic process. Different speed restriction policies and maintenance delay strategies are modelled and activated by the observed component states. Monte Carlo simulations are carried out to estimate the maintenance cost, the system benefit and the system downtime under different policies. Numerical results show the maintenance decision variable trade-off