Parameter Function (parameter + function)

Distribution by Scientific Domains


Selected Abstracts


Open-circuit voltage increase dynamics in high and low deposition rate polymorphous silicon solar cells

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2010
E. V. Johnson
Abstract The dynamics of the open-circuit voltage (VOC) of polymorphous silicon (pm-Si:H) solar cells deposited at high and low rates (8 and 1.5,Å/s, HR and LR) and containing lightly or heavily doped p-layers (LD or HD) are compared through in situ, variable intensity measurements during light-soaking (LS). The VOC's of the LR cells show an increase with LS, regardless of doping level, whereas the HR cells show decreasing VOC's. This result is in contrast to the changes predicted by the dark diode characteristics, which predict increasing VOC for all the devices. The device measurements are compared to the analogous measurements on co-deposited coplanar p,i layer stacks to determine whether the VOC dynamics can be linked to changes in the p-layer doping efficiency during LS. The changes to the macroscopic electrical behaviour of the cell under varying light conditions are modelled using a simple, three parameter function, and are compared to results from a detailed, numerical modelling tool, AFORS-HET. [source]


Reversible coagulation,fragmentation processes and random combinatorial structures: Asymptotics for the number of groups

RANDOM STRUCTURES AND ALGORITHMS, Issue 2 2004
Michael M. Erlihson
Abstract The equilibrium distribution of a reversible coagulation-fragmentation process (CFP) and the joint distribution of components of a random combinatorial structure (RCS) are given by the same probability measure on the set of partitions. We establish a central limit theorem for the number of groups (= components) in the case a(k) = qkp,1, k , 1, q, p > 0, where a(k), k , 1, is the parameter function that induces the invariant measure. The result obtained is compared with the ones for logarithmic RCS's and for RCS's, corresponding to the case p < 0. © 2004 Wiley Periodicals, Inc. Random Struct. Alg. 2004 [source]


Antibody response to Pseudomonas aeruginosa in children with cystic fibrosis

PEDIATRIC PULMONOLOGY, Issue 4 2009
Lucimar G. Milagres PhD
Abstract Cystic fibrosis (CF) is the most frequent life threatening autosomal recessive disease in white subjects. The primary cause of morbidity and mortality in children with CF is chronic pulmonary infection, mainly caused by Pseudomonas aeruginosa. The purpose of this study was to assess the value of the measurement of antibodies to P. aeruginosa in diagnosing lung infection by the bacteria in CF patients. We assessed P. aeruginosa antibody titers in CF patients from Rio de Janeiro, Brazil, using cell lysate antigens as well as recombinant PcrV, a Type III Secretion System protein. Sputum (more than 70% of the specimens) or oropharyngeal swabs were obtained whenever patients were regularly followed for their pulmonary disease. Blood samples were obtained with an average interval of 6 months for a period of 2 years. The ELISA cut-offs were assigned as the positive 95% confidence interval of the mean antibody levels from non-fibrocystic controls. Our data showed that most CF patients (81%) of whom were not chronically infected by P. aeruginosa (Groups I and II), had their first serology positive for rPcrV. Cell-lysate ELISA was able to detect P. aeruginosa antibodies before positive culture in the first serum sample of 44% of the patients from Groups I and II. When serum reactivity to rPcrV and cell lysate were combined, 94% of CF patients from Groups I and II (n,=,16) had the first serology positive for P. aeruginosa over a mean time of 20 months before the first isolation of P. aeruginosa. In conclusion, longitudinal P. aeruginosa serology should become part of respiratory care follow-up, in conjunction with other lung parameter functions. Pediatr Pulmonol. 2009; 44:392,401. © 2009 Wiley-Liss, Inc. [source]


Estimation methods for time-dependent AUC models with survival data

THE CANADIAN JOURNAL OF STATISTICS, Issue 1 2010
Hung Hung
Abstract The performance of clinical tests for disease screening is often evaluated using the area under the receiver-operating characteristic (ROC) curve (AUC). Recent developments have extended the traditional setting to the AUC with binary time-varying failure status. Without considering covariates, our first theme is to propose a simple and easily computed nonparametric estimator for the time-dependent AUC. Moreover, we use generalized linear models with time-varying coefficients to characterize the time-dependent AUC as a function of covariate values. The corresponding estimation procedures are proposed to estimate the parameter functions of interest. The derived limiting Gaussian processes and the estimated asymptotic variances enable us to construct the approximated confidence regions for the AUCs. The finite sample properties of our proposed estimators and inference procedures are examined through extensive simulations. An analysis of the AIDS Clinical Trials Group (ACTG) 175 data is further presented to show the applicability of the proposed methods. The Canadian Journal of Statistics 38:8,26; 2010 © 2009 Statistical Society of Canada La performance des tests cliniques pour le dépistage de maladie est souvent évaluée en utilisant l'aire sous la courbe caractéristique de fonctionnements du récepteur (, ROC , ), notée , AUC , . Des développements récents ont généralisé le cadre traditionnel à l'AUC avec un statut de panne binaire variant dans le temps. Sans considérer les covariables, nous commençons par proposer un estimateur non paramétrique pour l'AUC simple et facile à calculer. De plus, nous utilisons des modèles linéaires généralisés avec des coefficients dépendant du temps pour caractériser les AUC, dépendant du temps, comme fonction des covariables. Les procédures d'estimation asociées correspondantes sont proposées afin d'estimer les fonctions paramètres d'intérêt. Les processus gaussiens limites sont obtenus ainsi que les variances asymptotiques estimées afin de construire des régions de confiance approximatives pour les AUC. À l'aide de nombreuses simulations, les propriétés pour de petits échantillons des estimateurs proposés et des procédures d'inférence sont étudiées. Une analyse du groupe d'essais cliniques sur le sida 175 (ACTG 175) est aussi présentée afin de montrer l'applicabilité des méthodes proposées. La revue canadienne de statistique 38: 8,26; 2010 © 2009 Société statistique du Canada [source]