Vincent Couallier

Chain and conformation stability of solid-state DNA: implications for room temperature storage.

There is currently wide interest in room temperature storage of dehydrated DNA. However, there is insufficient knowledge about its chemical and structural stability. Here, we show that solid-state DNA degradation is greatly affected by atmospheric water and oxygen at room temperature. In these conditions DNA can even be lost by aggregation. These are major concerns since laboratory plastic ware is not airtight. Chain-breaking rates measured between 70°C and 140°C seemed to follow Arrhenius’ law. Extrapolation to 25°C gave a degradation rate of about 1–40 cuts/105 nucleotides/century. However, these figures are to be taken as very tentative since they depend on the validity of the extrapolation and the positive or negative effect of contaminants, buffers or additives. Regarding the secondary structure, denaturation experiments showed that DNA secondary structure could be preserved or fully restored upon rehydration, except possibly for small fragments. Indeed, below about 500 bp, DNA fragments underwent a very slow evolution (almost suppressed in the presence of trehalose) which could end in an irreversible denaturation. Thus, this work validates using room temperature for storage of DNA if completely protected from water and oxygen.

Simultaneous assessment of average fragment size and amount in minute samples of degraded DNA

There is currently no method allowing routine characterization of minute amounts of degraded DNA samples such as those encountered in forensic science, archived tissues, ancient DNA, extracellular or stool DNA, and processed food. Here we describe and directly validate such a method based, on the one hand, on a generalized DNA random fragmentation model and, on the other, on two quantitative polymerase chain reaction (PCR) experiments using two different target sizes. The model also makes it possible to determine the minimum sample amount, the minimum mass average fragment size, and the maximum degradation time necessary to obtain a positive PCR.

Modelling Recurrent Events for Repairable Systems Under Worse Than Old Assumption

The objective of the work is to model the failure process of a repairable system under “worse than old”, or harmful repairs, assumption. The proposed model is founded on the counting process probabilistic approach and interprets harmful repairs as the accumulation of failures on the same system. Increase in the conditional intensity is rather induced by the number of previous repair actions than by time contrarily to virtual age models. The LEYP model is defined and some comparison with existing imperfect repair models is given. The explicit form of likelihood function is provided. A covariate-dependent model is defined in order to take the effect of internal or external factors, which may be constant or time dependent, into account. After a description of the estimation procedure for left-truncated and right-censored data using a multiple systems data set, we provide some useful formulae for prediction of the number of failures in a future period. An application to data from the water distribution system of the city of Oslo (Norway) is given.

Control of extended-spectrum β-lactamase–producing Enterobacteriaceae nosocomial acquisition in an intensive care unit: A time series regression analysis

BACKGROUND This study was undertaken to determine the temporal relationship between implementation of different interventions in an intensive care unit (ICU) and control of endemic nosocomial acquisition of extended-spectrum β-lactamase Enterobacteriaceae (ESBLE). METHODS This was a prospective observational study with time-series analysis of the monthly incidence of ESBLE and its predictors. In November 2007, after a 14-month baseline period, an intervention consisting of restriction of third-generation cephalosporins (3 GC) and increased use of alcohol-based hand rubs was implemented. In January 2008, an increased health care worker (HCW):patient ratio was also implemented. In March 2010, the ICU was closed, and patients were moved to a clean ICU. RESULTS The first intervention resulted in global reduction in 3 GC and increased use of alcohol-based hand rub. A significant change in ESBLE incidence was observed in a full segmented univariate regression analysis (mean change in level, -0.91 ± 0.19; P < .0001). After ICU closure, there was a dramatic reduction in ESBLE acquisition. According to the multivariate model, the ICU closure was the main protective factor. Before ICU closure, an increase in the HCW:patient ratio of 0.1 point tended to be associated with a decreased risk of ESBLE acquisition (relative risk, 0.28; 95% confidence interval, 0.06-1.25; P = .09). CONCLUSIONS This study shows that ICU closure was associated with, but not necessarily the reason for, control of ESBLE cross-transmission in a nonoutbreak setting. Environmental ESBE sources may play a role in cross-transmission.

Statistical modelling, planning and inference in accelerated trials

We consider the problem of statistical modelling and planning in accelerated trials to obtain the statistical inference for the main reliability characteristics of the product.

Calcul de MTBF des systèmes aéronautiques inspectés périodiquement soumis à rupture aléatoire de systèmes de régulation

Cependant, si l’état d’un ou plusieurs éléments peut influencer la fiabilité des autres éléments, l’hypothèse d’indépendance n’est plus correcte et le calcul classique de fiabilité du système comme mentionné précédemment n’est plus adapté. Le but de cette présentation est de développer, dans un modèle adapté aux données de maintenance aéronautique des systèmes embarqués (inspections régulières, testabilité imparfaite ou pannes masquées), les outils de calculs de fiabilité prévisionnelle et les prévisions de MTBF pour des systèmes maintenus dont certains composants ont une fiabilité dépendant de l’état d’autres composants, notamment quand un sous-système est censé réguler un paramètre (température, vibrations...) influençant la fiabilité des composants associés à une fonction principale.

An Approach to System Reliability Demonstration Based on Accelerated Test Results on Components

Reliability demonstration is often mandatory for industries that need to prove the quality of their production. In a reliability objective at the global system level, the basic use of standards such as MIL-HDBK-781 or IEC-60300 for reliability demonstration of each sub-system must be adjusted. Practitioners often have to fix high-level reliability goals (around 0.999) on each sub-system to guarantee that system reliability exceeds 0.8. Moreover, the confidence obtained for an overall reliability drops down to non-admissible values because of the multiplicity of testing procedures. We propose an approach, from k accelerated tests, to determine an optimized test time whilst ensuring that the reliability of a component system is greater than a goal value and by avoiding the too conservative method consisting in multiplying the confidence levels.